You may find this page helpful when you disagree with a decision HMRC have made.
This page explains the basics of the appeal process. We aim to help you work through all the stages of resolving a tax dispute with HMRC, including making an appeal to the independent tax tribunal.
We only cover direct tax, by which we mean things like income tax and National Insurance contributions; the definition of direct tax also includes other things that you might not expect, like student loan repayments.
If you disagree with an HMRC decision about indirect tax, for example VAT, the rules are very similar. You can find information on what to do on GOV.UK.
Another option that may be available to you when you disagree with a decision HMRC have made is Alternative Dispute Resolution. This can be used alongside the appeal process.
This page does not cover the following:
- HMRC are hassling you for information you know you ought to give them or HMRC have discovered something you had not told them. You will have to sort that out with HMRC. Please go to our information on enquiries.
- If your dispute is about tax credits, go to the tax credits and benefits section of our LITRG website, or the HMRC guidance on GOV.UK.
- HMRC are demanding money that you owe, but you cannot afford to pay.
If you disagree with HMRC and you have a right of appeal, you can make an appeal in writing to HMRC. You must normally make an appeal within 30 days of HMRC’s notice of their decision.
HMRC will consider your appeal. They will either agree with you and amend their decision or confirm their original decision. They will confirm their position in writing. You will have 30 days from the new decision to appeal, if you still do not agree with HMRC.
If you cannot agree your position with HMRC, HMRC may offer you a review. You can request a review at any time. A review is an internal process, carried out by another HMRC officer, not previously involved in your case.
If you still cannot agree your position with HMRC after a review, or do not want a review, you can appeal to the First-tier Tribunal. The tribunal will make a decision about your case. If you disagree with the tribunal’s decision, you may be able to make a further appeal. If you take your case further, you may have to pay HMRC’s costs as well as your own, so you should think carefully before doing so.
You can make an appeal if you have the right to appeal against an HMRC decision. You may have a right of appeal where HMRC, for example:
- are looking into your tax affairs and demanding excessive amounts of information or taking too long without bringing their enquiries to an end;
- have altered your Self Assessment (see our LITRG website) after an enquiry because they think you got it wrong;
- have made an assessment of tax on you or are disallowing a claim to a relief;
- have refused you a sub-contractor's certificate;
- have issued a coding notice, which you think is wrong;
- are demanding a penalty or surcharge which you think is unfair or incorrect.
When HMRC write to you with a decision, they should also tell you whether or not you have a right of appeal. If you do not know whether you have a right of appeal, ask HMRC in writing.
If you do not have a formal right of appeal (for example, if HMRC refuse to apply one of their extra-statutory concessions) but disagree with an HMRC decision or the way they have handled your case, there are other options:
See our guidance on how to make a complaint to HMRC, and then to an independent body if HMRC do not satisfactorily resolve the matter.
The courts can review the lawfulness of decisions or actions by a public body through the judicial review process. This can be an expensive procedure and expert legal representation is needed. There are strict time limits for commencing judicial review procedures. There is a very useful basic guide to the judicial review procedure on the website of the Public Law Project.
If you wish to appeal a decision, you must send a notice of appeal to HMRC.
You must do this within 30 days of the date of HMRC's notice of their decision. HMRC’s decision notice may be in the form of a letter, but it could also be an assessment, penalty notice or other document.
If you make your appeal more than 30 days after the date of the decision, HMRC might still agree to consider your late appeal. If HMRC do not accept your late appeal, you can apply to the tribunal to decide whether your late appeal should be allowed.
Your appeal must be in writing. You can either use an appeal form, or you can write your own letter of appeal. An appeal form may have been sent to you with the HMRC decision notice.
You must provide the following information with your appeal:
- your name, or the name of your business – whichever is relevant
- your reference number, which is shown on the HMRC decision notice
- what decision or assessment you are appealing against
- why you disagree with HMRC's decision (your ‘grounds for appeal’);
- what you think the outcome of the case should be – for example, if an amount of tax is disputed, say what you think the correct figures should be and how you have worked them out.
If you are not sure why you disagree or cannot work out the correct figures that should not stop you putting in an appeal. Just try to explain as best you can – for example, if you think you have a reasonable excuse for failing to get your tax return submitted on time, give as much detail as you can about what happened, when and why.
HMRC will consider your appeal and let you know if they agree with you. Sometimes they will want to discuss your case with you, for example, they might want you to provide more information to back up your appeal.
HMRC may agree with your appeal and amend their decision.
If HMRC do not agree with your appeal, they will normally offer to review their decision. This review process is carried out by another HMRC team that is independent of the people within HMRC who made the original decision.
If HMRC do not offer to review their decision, you can ask them to do so, and you can do so at any time.
If you cannot agree with HMRC after making your appeal, you can make an appeal to the tribunal. You cannot have a review and a tribunal appeal at the same time.
If HMRC do not agree with your appeal, they will normally offer you a review of their decision. You can then decide whether you want to accept their offer, or whether you would prefer to take your appeal straight to the tribunal. You have 30 days from the date of HMRC’s offer of a review to accept it.
If HMRC do not offer you a review, you can ask for one. This is a useful safeguard if the discussions with HMRC drag on without getting anywhere, or you hear nothing from HMRC.
If you ask for a review, HMRC usually have 30 days from receipt of your request to say whether or not they agree with your view. They may only take longer to respond if it is reasonable for them to do so. If they do not agree with you, they must proceed with the review.
What should I send to HMRC when asking for a review?
If you ask HMRC for a review, you should make sure that you include in your request for a review as much information as you can. For example, you should say why you think the original decision is wrong, and if there is any further information that the original HMRC decision-maker might not be aware of, this is your opportunity to provide it.
For example, if you are claiming that you have a reasonable excuse for filing your tax return late, but HMRC do not already have all of the facts about what happened, explain the situation again. You should try to give as much information as you can and if you have any supporting evidence, send copies of it with your review request.
Let’s say you spilled a cup of coffee over your laptop computer on 30 January when you were going to file your tax return, so you could not complete it. You took the laptop for repair the next day, got it fixed within a week and then filed your tax return as soon as possible when it was back up and running (so you put matters right as soon as you could).
HMRC in their original decision have said they do not think you had a reasonable excuse as they thought you should have asked a friend or family member if you could borrow their computer; or used a public computer such as at a local library.
In your request for a review, you should send in any further evidence you have. You could send a copy of the repair bill for the laptop as evidence of the problem. Then you could explain that your library does not provide the facilities they suggest and in any event it was closed on both 30 and 31 January as it now only opens on Tuesdays and Thursdays. Furthermore, you think it is not reasonable for HMRC to suggest you rely on friends or family to deal with your private tax affairs. Perhaps also the information you needed to complete your tax return was saved on the computer that was damaged and you needed it to be repaired before you could access it.
Giving such further information could make all the difference to the outcome of the review.
Who carries out the review?
HMRC's internal reviews are carried out centrally from their Solicitors Office and Legal Services team, by someone within HMRC who is independent of the original HMRC decision-maker. That means the reviewer is not within the management chain of the original decision maker
For instance, appeals about Self Assessment or PAYE – for example, whether you have a reasonable excuse for filing your tax return late, or if you disagree with a PAYE coding – will go to a specialist office.
Compliance reviews, for example, where you are challenging HMRC's wish to inspect documents or other things at your premises, are generally dealt with by someone removed from the original decision, in what HMRC call their ‘local compliance offices’, although in reality they might not be ‘local’ to you at all.
If I do not want a review, can I appeal to the tribunal?
Internal reviews are optional. If you prefer, you can appeal straight to the tribunal, but normally in direct tax matters you must also notify HMRC before – or at the same time as – you do so. However, an internal review is worth considering as an alternative way of resolving your dispute, as it could save time and costs of appealing your case to the tribunal.
If I opt for a review and then change my mind, can I appeal to the tribunal?
If you have opted for a review, you cannot take your case to the tribunal until the review is concluded.
What happens with a review?
The reviewer will have another look at the case and decide whether or not he or she agrees with the original decision. They will write and tell you the outcome. This should be within 45 days unless HMRC agree an extension with you. Their usual practice is to extend it for a further 45 days, so the review is completed within 90 days.
The outcome might be one of three things:
- that the reviewer agrees with you and cancels HMRC's original decision;
- that they agree with you in part and vary HMRC's decision;
- or that they agree with HMRC's original decision and turn down your appeal.
As mentioned above, if the reviewer has not made a decision within 45 days, they should tell you. They might ask for more time. You do not have to agree, but it might be in your interest to do so if ultimately your case is resolved more quickly. If you do not agree to allow the reviewer more time, they must give you a notice saying that the review is concluded without a decision being reached and you can then appeal to the tribunal if you wish.
What if I disagree with the reviewer's decision?
Once the review is concluded, if you do not agree with the outcome, you have a further 30 days, from the date of the review conclusion letter, to appeal to the tribunal.
The tribunal system is completely independent of HMRC.
HMRC are one party to an appeal and you are the other.
You make an appeal to the Tax Chamber of the First-tier Tribunal. Exceptionally, tax appeals may be heard by the Upper Tribunal, but that is only if the law involved is particularly complex.
To make your appeal, you will need to fill in a form. You can do this:
- online via GOV.UK; or
- you can fill in a paper form. If making your appeal on paper, the type of form depends on whether you are applying to close an HMRC enquiry, or appeal another matter. See GOV.UK for a full list of tax appeal forms and guidance notes.
Note that if you are a Scottish taxpayer or Welsh taxpayer, HMRC (rather than Revenue Scotland or the Welsh Revenue Authority) continue to administer direct taxes such as income tax. You therefore still need to appeal to the UK-wide Tribunal service for direct tax matters.
The answer is: it depends on your case and how it is dealt with.
There are a number of differences between the First-tier and Upper Tribunals, but the main one is the costs regime, known in Scotland as expenses.
What is the First-tier Tribunal costs regime?
In the First-tier Tribunal, each party normally pays their own costs, and cannot be made to pay the costs of the other party, even if they lose. That means that you will have to fund your own appeal, but you will not normally risk having to pay HMRC's costs.
But the First-tier Tribunal may award costs where one party to the case has acted unreasonably in bringing, defending or conducting the proceedings. This means if the tribunal thinks you acted unreasonably, they can order you to pay HMRC's costs in defending the case.
Of course, if HMRC act unreasonably, the tribunal can make HMRC pay your costs.
The First-tier Tribunal can order a party to pay wasted costs incurred because their representative has acted improperly or unreasonably, or been negligent.
If your case is to be treated as complex, it may be heard in the Upper Tribunal rather than in the First-tier Tribunal.
Also, if you or HMRC appeal against the First-tier Tribunal's decision, the appeal will be heard by the Upper Tribunal.
What is the Upper Tribunal costs regime?
In the Upper Tribunal, there is a costs regime where the losing party generally pays the costs of the winning party as well as its own. However, you can, if you wish, opt out of the costs regime, in which case each party will pay its own costs, and neither party will have to pay the costs of the other, whatever the result.
In short, you can either play safe by opting out, or you can take a chance that you will recover your costs if you win, but at the same time risk a large bill for HMRC's costs if you lose. The choice will be yours.
You will be notified if your case has been allocated to the complex track and must notify the Tribunal within 28 days of receiving the notice if you want to opt out of the costs regime.
You also have the right to object to the case being heard in the Upper Tribunal.
The tribunal is able to strike out your case if you repeatedly fail to follow their directions. Striking out your case means that HMRC automatically win.
If HMRC repeatedly fail to follow the tribunal's directions, the tribunal can bar them from taking part in any further proceedings.
HM Courts & Tribunals Service provide guidance (leaflet T242) on what happens after you make your appeal and on what happens at a hearing. We recommend that you read this in addition to our guidance below.
At the level of the First-tier Tribunal, there are different ways in which your case can be handled depending on the facts, such as what it is you are appealing about and how complex your case is.
Some cases are usually dealt with on paper. This means that the tribunal will just review papers submitted by HMRC and by you, and make their decision from those.
If your case is to be dealt with in this way, it is important that your papers are neat and tidy so that the tribunal can follow them. Read How do I prepare my case?, which guides you through organising your papers. If you are told your case will be dealt with on paper, but you would prefer to have a hearing, you can request one.
If you have any special needs which might need to be catered for at the hearing, for example a disability, you should tell the tribunal in advance.
Normally you have 30 days from the date of HMRC's decision notice in which to tell HMRC you wish to appeal.
HMRC can agree to consider a late appeal and will generally do so if you have a good reason for not meeting the deadline. If HMRC do not agree to consider a late appeal, you can apply to the tribunal to accept your appeal. HMRC will usually agree to a withdrawal of an appeal if you change your mind later.
Once you have lodged your appeal with HMRC within 30 days of the decision notice, you do not have to worry about taking your appeal to the tribunal within any time limit. But if you have opted for internal review and wish to appeal against the decision of the review team, you only have 30 days from the date of that decision to appeal to the Tribunal.
Before appealing, you should know that if your appeal proceeds to a tribunal hearing, it will probably be heard in public.
This will be true whether your case is allocated to the First-tier or Upper Tribunal.
In both cases, human rights law requires public hearings as a general course.
You can apply for privacy on the grounds that a private hearing is necessary because, for example, minors are involved, or for the protection of your private life, or because publicity might affect a fair and just hearing.
Most legal proceedings, not just tax, are in public. It is very unlikely that you will find crowds of curious spectators or reporters at the hearing: most simple tax appeal hearings are attended by only the parties to the cases. More complex cases may be attended by one or two specialist tax reporters.
If you really think that there is a special case for your hearing to be held in private, you should make a request to HM Courts & Tribunals Service in plenty of time before the hearing date.
Making an appeal does not mean that you can simply not pay the tax in dispute.
There are three main options:
- Normally, you will pay the tax when it is due.
- While your appeal is being dealt with, you could pay the correct amount of tax you consider is due.
- You can apply to HMRC asking them to agree to a postponement of the disputed tax. You should apply by writing to HMRC at the address on the decision notice. If HMRC refuse your postponement request, you can appeal to the tribunal and ask for them to decide.
It may not always be advisable to ask for a postponement or pay only the amount of tax you consider is due. If you lose, you will probably have to pay interest on the late-paid tax in addition to the tax itself.
If you pay all the tax due on time, but then win your appeal, you may receive some extra interest as well as the repayment of the tax you have overpaid.
You can settle an appeal by agreement with HMRC. Given that HMRC have an internal review process, you are unlikely to proceed to formal appeal if you can resolve the dispute by agreement.
If you make an appeal to the tribunal, you need to prepare your case. It takes a lot of time to prepare properly.
It may take time for the appeal to be listed for hearing. You will usually have at least 14 days' notice of the hearing date, unless you agree otherwise, or in urgent or exceptional circumstances.
The guide below is for people who cannot afford to pay for professional advice. If you can afford to pay, we suggest that you consult your tax adviser, if you already have one. If you are not represented by a tax adviser, you can find one using the Chartered Institute of Taxation website.
Are there public funds available?
In a few cases, you may have the right to help from public funds in fighting your case:
- The appeal concerns penalties that the courts have declared to be criminal within the terms specified by the European Convention on Human Rights or where you want to argue that issue.
- It is in the interests of justice that you should be legally represented.
- You are financially eligible for funding.
In practice, funding is most likely to be available where you are disputing a penalty, which is substantial either in terms of its amount or its impact, and which has been imposed in addition to the tax you have to pay.
If you think you may be eligible for public funds, ask HMRC for a copy of the factsheet The Human Rights Act and Penalties.
Where can I find free advice and representation?
The following charities specialise in giving free tax advice to people on low incomes, who cannot afford to pay a professional adviser:
Please be aware that the above charities might not be able to support your case right through the appeal process and they may not be able to help you if you do not meet their criteria as low-income and/or older taxpayers.
You could ask for advice from a local Citizens Advice Bureau.
Representation at a hearing is harder to come by, but the Bar Pro Bono Unit helps put potential clients in touch with barristers who are prepared to handle a case for no fee.
How do I help the person giving me advice?
If you do seek help, make it easy for the person providing it. That will make it cheaper, if you are paying, and quicker and better, whether you are paying or not.
- Prepare a summary, which explains the main points and asks the questions you want answered.
- Provide copies of all relevant correspondence with HMRC, in date order and filed or stapled together so it is easy to handle.
- If accounts are important, make sure they are clear and preferably professionally prepared.
- Do not supply scraps of paper or unexplained bills or bank statements in the hope that the adviser will sort it all out and make sense of it.
This preparatory work you do will not only help your adviser but will be valuable in preparing your case to be presented to the tribunal.
Bear in mind that you might need to submit papers and documents to the tribunal before the hearing, or if your case is to be dealt with exclusively on paper. The tribunal will tell you if you need to do so and will give you a time limit. Make sure you take careful note of this and meet it.
How do I put my file together?
The object is to have a single file, for example, a ring binder, which contains all your witness statements, copies of the documents you need to refer to and your 'skeleton argument' (see below) of the issues of your case. If there are a large number of documents or papers, you may need more than one folder, but for most cases one should be enough.
HMRC may be preparing a similar file. The hearing will proceed more smoothly if you can agree with HMRC on a single file containing all the material needed by both sides. Keep in touch with HMRC, because you share a common interest in having the case settled.
You may be able to agree with HMRC a common statement of facts, which can then be used as the basis for the appeal without having to be proved by evidence.
You should number the pages in the file, so that when you refer to a page during the hearing, everyone present who has one of your files is looking at the same thing.
You can use dividers to separate the file into sections, but if you use them, make sure that every file has the same divisions.
Since you are making the appeal, generally you must prove your case based on the facts. If you do not succeed in this, you will probably lose the appeal.
What are witnesses and witness statements?
Any fact on which you rely, and which HMRC has not agreed, will have to be established as correct by you. Sometimes documents will help, sometimes evidence from a witness, and sometimes both together.
You are likely to be your own most important witness, and you may be the only witness. You must think carefully about what you will say.
You and any other witnesses are likely to be cross-examined by the person handling the case for HMRC.
It is unlikely that you will want to call a witness who is unwilling to give evidence. But if you do, you can apply to the tribunal for a witness summons saying why you require that particular witness to attend. If your application is granted, the tribunal can state that you must be responsible for the witness's necessary expenses of attending the hearing.
Witness statements are helpful, as they set out, in numbered paragraphs, the evidence the witness is giving. For example, they might say something like:
‘On April 1 20XX I had a meeting with ABC and a copy of a note I made immediately afterwards is at page XXX in section A2 of the file.’
Start writing your own witness statement as early as possible, making sure it covers everything you said or did or were told, and which matters for the purpose of your case. The statement should deal with each fact in date order.
If you are calling other witnesses, help them to make similar statements of their evidence, but make sure they are in their own words and not yours.
Ask HMRC whether they will be calling any witnesses. If they are, it is sensible to exchange copies of witness statements ahead of the hearing. If they are not calling witnesses, you should still let them have copies of your witness statements.
Make sure that references to the witness statements are properly indexed.
What are skeleton arguments?
Skeleton arguments summarise the relevant legal and technical issues and apply them to the facts you hope to prove. They are not easy to prepare, but help enormously at the appeal hearing.
The purpose of them is basically to set out how you understand the law should apply to your circumstances and it should give details of the relevant tax law and any other decided cases from the tax tribunals or higher courts that might support your own case.
It should make reference to supporting documents within your bundle of papers for the case, where possible.
Bear in mind that collecting together and then explaining your points is particularly hard where the appeal hearing is contested. It is much better to do so in advance and to write them down.
It is helpful to include copies of any legislation you use in the file for the hearing, and this applies also to relevant extracts from any other similar cases to which you wish to refer.
Do not be intimidated by unfamiliar language. The point is to show how the law can be applied to the facts of your case. You can certainly refer to pages of textbooks to support your case rather than using the formal legislation. HMRC's guidance and manuals on GOV.UK can be very helpful in providing information.
Other ways to get ready for a tribunal hearing
You might want to ask HM Courts & Tribunals Service whether there are any earlier cases you can attend just to listen and watch. Their office will tell you if you telephone them. GOV.UK gives full contact details.
Rehearse your case in front of family or friends or, better still, any professional who will give you the time. This may help you to identify weak points, which you can clear up before the hearing.
HM Courts & Tribunals Service provide guidance (leaflet T243) on what will happen at the hearing, and GOV.UK has some simple information, all of which we recommend you read in addition to our notes. One important point to remember is that you can take someone along with you, even if they are only there for moral support.
Depending on how your case is being dealt with, proceedings of the tribunal may vary in formality, but the following gives an outline of how the hearing might flow.
Opening the meeting
Turn up in good time for the meeting. Aim to arrive at least half an hour or three-quarters of an hour beforehand. Make sure you know in advance exactly where you have to go and how to get there. Make sure any witnesses you want to call come too.
Bring with you your files, with sufficient copies for the tribunal, for your HMRC opponent, and preferably one for witnesses to refer to. You should check beforehand how many copies the tribunal will need. Each set should be in a file containing exactly the same material as the others.
The Chair of the Tribunal will probably introduce all the members of it and will explain how the proceedings are to be conducted.
Make sure that each tribunal member and your opponent has a copy of your file.
Setting out your case
You will probably be invited to open your appeal by explaining what it is about. When you explain your appeal, take everyone through your file so that they can see how it is arranged and what it contains.
After you have explained briefly what your appeal is about, you will call your witnesses, starting with yourself.
You must be clear when you are giving evidence as a witness and when you are addressing the tribunal as the person making the case, but the Chair will help you.
When you give evidence, it will probably be enough to refer to your written statement and say that it is true. You probably will not be asked to read it out, but if you are asked, you must do so.
When you have finished, you will be cross-examined by HMRC. HMRC’s purpose in the cross-examination will be to check the truth of what you have said and to put HMRC's case to you, so far as it conflicts with the facts as you give them.
Remain calm and answer the questions honestly and simply. You may make a note of the questions asked and of your answers. The Chair or other members of the tribunal may ask you questions as well.
When the cross-examination is finished, you may raise a few extra points that have arisen from it. Try to keep any additional comments very short, and make sure the Tribunal can make a note of the points you are making.
After that, if you have any other witnesses, you can call them and refer them to their statements and ask them to add to any point you think worth stressing. Then they may be cross-examined by HMRC, and you should listen carefully to the questions and answers and note down the important ones.
When HMRC have finished, you can ask the witnesses additional questions to help explain anything which seems to call for further explanation as a result of the cross-examination.
Provided you will have the right to address them again when your opponent has finished, you should tell the tribunal that your case is complete once you have called all your witnesses. If you are told that you will not have that right, then you should say that you want to make your closing points.
HMRC's or another opponent's case
It will then be the turn of HMRC to explain their case and call their witnesses. If they call any witnesses, you will have the right to cross-examine each of them when they have been taken through their witness statements.
You should have received their statements in advance, and prepared in advance the questions you want to ask them. Your cross-examination should always be calm and polite and should probe their account of events where it differs from yours or that of your witnesses.
Try to note down your questions and the answers you are given.
After HMRC's witnesses have finished, HMRC will probably sum up their case. They will go through the relevant evidence, say what they think the facts of the case are and explain how they consider the law relates to those facts. If HMRC have a skeleton argument, you will probably have seen it in advance and HMRC are likely to base their comments upon it.
The last word
Normally you will be given the last word. This is when you will use your skeleton argument.
The idea is to say the evidence has proved how the law applies to the facts of your case and why you consider that you should win your appeal. Members of the tribunal may ask you questions, and you should listen to them carefully and answer them to the best of your ability.
Breaks for lunch or overnight
It is quite likely that there will be a break at lunchtime.
If any of your witnesses is in the middle of giving evidence at that time, you should not talk to them during the lunch break.
If your case lasts more than one day, there will be an adjournment at the end of the first day. The same principles apply as during the lunch break.
Make use of the breaks to assess whether you need to adjust your plans.
When the case is finished
When the case is finished, the tribunal may give their decision straight away, or may say that they will send it in writing. Even if the tribunal give their decision straight away, they will send you a written decision notice stating the decision and notifying you of any further right of appeal.
The First-tier Tribunal must give you their decision notice within 28 days of making their decision and provide either a summary or full statement of agreed facts and reasons for the decision.
The Upper Tribunal must send a decision notice within a reasonable time of concluding the case and give their reasons unless the parties agreed to the decision or agreed not to be given reasons.
If your case is heard by the First-tier Tribunal, and they tell you at the hearing that you have lost, you should there and then express your disagreement, by saying 'I wish to record my dissatisfaction with your decision.'
You will then be free to embark on the process of a further appeal if you so decide. This is time-consuming. We do not cover the process in this guide.
If you wish to make an appeal to the Upper Tribunal or higher, you first have to apply for permission to appeal – see guidance on GOV.UK. If you are given permission, GOV.UK then further explains the appeal to the Upper Tribunal.
You should think very carefully before you decide to make any further appeal. An appeal to the First-tier Tribunal involves little risk of your having to pay substantial costs. If you make an appeal to the Upper Tribunal, or above, you may have to pay HMRC's legal costs as well as your own if you lose. The amounts could be considerable.