UK HMRC Enquiry Survival Guide 2026/27
HMRC enquiries 2026/27: the s.9A enquiry window, discovery time limits, Schedule 36 information notices, inaccuracy penalties, reviews, ADR and tribunal appeals.
An HMRC compliance check can be an informal letter or a formal notice of enquiry under section 9A of the Taxes Management Act 1970. This guide sets out the time limits HMRC works to, its information powers under Schedule 36 Finance Act 2008, how inaccuracy penalties are set under Schedule 24 Finance Act 2007, and your routes to challenge a decision.
How far back HMRC can assess (Income Tax and CGT)
| Situation | Time limit after the end of the tax year | Authority |
|---|---|---|
| Ordinary case | 4 years | TMA 1970 s.34 |
| Loss of tax brought about carelessly | 6 years | TMA 1970 s.36(1) |
| Offshore matter or offshore transfer | 12 years | TMA 1970 s.36A |
| Deliberate, failure to notify, certain avoidance cases | 20 years | TMA 1970 s.36(1A) |
Inaccuracy penalty ranges (domestic matters)
| Behaviour | Maximum | Minimum, prompted | Minimum, unprompted |
|---|---|---|---|
| Reasonable care taken | 0% | 0% | 0% |
| Careless | 30% | 15% | 0% |
| Deliberate but not concealed | 70% | 35% | 20% |
| Deliberate and concealed | 100% | 50% | 30% |
FA 2007 Schedule 24 paragraphs 4 and 10. Disclosure is unprompted only if you had no reason to believe HMRC had discovered, or was about to discover, the inaccuracy (paragraph 9(2)).
If a letter arrives
- Read what is being checked and note every deadline in the letter.
- If you have an accountant, HMRC will normally deal with them.
- Answer what is asked, on time, or ask for more time before the deadline passes.
- If you find an error yourself, tell HMRC: the quality and timing of disclosure set where the penalty lands.
- Keep copies of everything you send and receive.
Frequently asked questions
What is an HMRC enquiry and how does it start?
A formal enquiry into a Self Assessment return starts with a notice of enquiry under section 9A of the Taxes Management Act 1970 (for a company tax return, Finance Act 1998 Schedule 18 paragraph 24). If you filed on time, HMRC must give the notice within 12 months after the day you filed. If you filed late, or amended the return, the window runs to the next quarter day (31 January, 30 April, 31 July or 31 October) after the first anniversary of filing or amending. An enquiry can cover the whole return or one item. Once that window has closed, HMRC can only reopen a year by a discovery assessment, which has its own time limits.
How far back can HMRC go?
For Income Tax and Capital Gains Tax, an assessment can normally be made up to 4 years after the end of the tax year (TMA s.34), 6 years where the loss of tax was brought about carelessly (s.36(1)), and 20 years where it was deliberate, where you failed to notify chargeability, or in certain avoidance-scheme cases (s.36(1A)). Where the lost tax involves an offshore matter or offshore transfer, the limit is 12 years (s.36A), unless HMRC had received overseas information in time to act sooner. Inheritance Tax and VAT have their own 4, 6 and 20-year rules.
What information can HMRC demand in an enquiry?
Under Finance Act 2008 Schedule 36, HMRC can by written notice require you to provide information or documents reasonably required to check your tax position (paragraph 1), and can require a third party to do so about you (paragraph 2). It can inspect business premises, normally at an agreed time or with at least 7 days' notice. A notice cannot require legally privileged material, and auditors and tax advisers have protections for certain papers. You can appeal against a taxpayer notice within 30 days, except for items that are part of your statutory records. Failing to comply can cost £300, then up to £60 a day; inaccurate information can cost up to £3,000 per inaccuracy.
What counts as a reasonable excuse against a penalty?
GOV.UK gives examples that may count, including the death of a partner or close relative shortly before the deadline, an unexpected hospital stay, a serious illness, a computer or software failure while preparing an online return, HMRC online service problems, fire, flood or theft, unforeseeable postal delays, delays linked to a disability or mental illness, being unaware of or misunderstanding the obligation, and relying on someone else who did not file. It says these will not count: a payment failing for lack of funds, finding HMRC online systems too hard, not getting a reminder, or a mistake on the return. You must put things right as soon as the excuse ends.
What is Alternative Dispute Resolution with HMRC?
ADR is a free, non-statutory process in which a trained HMRC mediator who is not the officer on your case helps you and that officer resolve a dispute. It can be used when an enquiry has stalled, there is a dispute about facts or communications have broken down, and it does not affect your right to appeal or ask for a review. HMRC can refuse an application. It is not available for, among other things, cases with HMRC criminal investigators, tribunal cases categorised as paper or basic, automatic late filing or payment penalties, the High Income Child Benefit Charge, or civil evasion penalties.
How do reviews and First-tier Tribunal appeals work?
You usually have 30 days from a decision letter to appeal to HMRC. If HMRC does not change its decision, it will offer a statutory review; you have 30 days to accept it or appeal to the tax tribunal. Reviews usually take 45 days. If you disagree with the review result, you can usually appeal to the tribunal within 30 days of the review letter, using form T240. The tribunal allocates each case as Default Paper, Basic, Standard or Complex. If an enquiry has dragged on, you can apply to the tribunal on form T245 for a direction that HMRC issue a closure notice (TMA s.28A(4)).
How are inaccuracy penalties calculated under Schedule 24 FA 2007?
The penalty is a percentage of the potential lost revenue. The maximum is 30% for a careless inaccuracy, 70% for a deliberate one and 100% for a deliberate and concealed one. HMRC must reduce it to reflect the quality of your disclosure (telling HMRC, helping it quantify the error and giving access to records, plus timing), but not below a floor: 15%, 35% and 50% if the disclosure was prompted, and 0%, 20% and 30% if it was unprompted. There is no penalty where you took reasonable care. Higher maximums, up to 200%, apply to some offshore matters. A careless-inaccuracy penalty can be suspended for up to two years if you meet conditions HMRC sets.
What does interest add to an enquiry settlement?
Interest runs on tax paid late from the date it was due to the date it is paid. HMRC's late payment rate is the Bank of England base rate plus 4 percentage points; HMRC set it at 7.75% from 9 January 2026. If HMRC finds you owe more at the end of a check, it will ask you to pay within 30 days. If you cannot pay, tell the officer and ask about a payment plan.
How do I complain about how HMRC handled my case?
A complaint is about service, such as delays, not about the tax decision itself (use an appeal or review for that). HMRC first carries out a first-tier review, and you can ask for a second-tier review by a different person. If you are still unhappy you can ask the Adjudicator's Office, which is free and independent of HMRC, and after that ask your MP to refer the complaint to the Parliamentary and Health Service Ombudsman.