United Kingdom: Your responsibility

An adviser can prepare the claim, write the technical narrative and complete the additional information form, and every agent involved is named on that form.1Source 1HMRC, Submit detailed information before you claim Research and Development (R&D) tax relief (26 September 2025); HMRC manual CIRD182000 (25 August 2026). None of that moves the claim out of the company's name. The claim is made in the Company Tax Return, the company signs the return, and HMRC's penalty for an inaccuracy is charged on the person who gives the inaccurate document, which is the company.2Source 2HMRC Compliance Handbook CH81010 (7 October 2026): the penalty is charged on the person who gives the inaccurate document (Finance Act 2007 Schedule 24 paragraph 1). The questions on who signs the claim and can we see the full claim before filing? are about making that responsibility real. The people who did the work read the technical descriptions before the form goes in, and the company keeps a copy of what was filed.

• Making or amending a claim. For accounting periods beginning on or after 1 April 2023, an R&D claim can be made, amended or withdrawn within a fixed period. It ends on the last day of the two years beginning with the last day of the period of account. HMRC has a discretion to accept late claims in limited cases.3Source 3HMRC manual CIRD81800 (25 August 2026), Finance Act 1998 Schedule 18 paragraph 83E. An unsolicited offer to claim for earlier years should be tested against these dates (cold calls about unclaimed refunds).
• Amending the return. Changes to a Company Tax Return must usually be made within 12 months of the filing deadline.4Source 4HMRC, Company Tax Returns: making changes.
• HMRC's enquiry window. HMRC can open an enquiry into the return within 12 months of the day it was delivered, and later for a return delivered late. For a member of a group that is not small, the 12 months run from the statutory filing date.5Source 5HMRC Enquiry Manual EM1510 (30 September 2026), Finance Act 1998 Schedule 18 paragraph 24.
• Discovery assessments. After the enquiry window, HMRC can make a discovery assessment within 4 years from the end of the accounting period, 6 years where tax was lost through careless behaviour, and 20 years where it was deliberate.6Source 6HMRC Compliance Handbook CH51300 and CH56200 (7 October 2026), Finance Act 1998 Schedule 18 paragraph 46. A claim can therefore be looked at well after the relief has been paid, which is why review support in the engagement letter matters (is review support included?).

If HMRC reduces a claim that has already been paid, your company repays the full amount overclaimed. Interest on an overpaid credit runs from the date it was paid until it is repaid, for accounting periods beginning on or after 1 April 2023.7Source 7HMRC, Tell HMRC if you've claimed too much Research and Development (R&D) tax relief (14 August 2026). A penalty for an inaccurate return can be charged, from 0% to 100% of the potential lost revenue depending on whether the inaccuracy was careless or deliberate and how it came to light.8Source 8HMRC, Compliance checks: penalties for inaccuracies in returns or documents, CC/FS7a (21 July 2026). Whether the adviser's fee comes down too depends on the engagement letter, not on HMRC: see what happens to the fee if the claim is reduced?

There is one exception that works in the company's favour. Where a third party deliberately supplied false information or withheld information, HMRC can penalise that third party; the company is still penalised if it did not take reasonable care over the information it gave.9Source 9HMRC Compliance Handbook CH81166 (7 October 2026), Finance Act 2007 Schedule 24 paragraph 1A. The lesson is practical: take reasonable care, which means reading the claim and keeping the records, and do not rely on the adviser's name to carry the penalty.

If the company finds that it has claimed too much, HMRC guidance sets out how to tell it: by amending the return if the time limit for amendment is still open, or through HMRC's online disclosure service where it is not. The company's offer will usually be the full amount it owes, including tax, credits to repay, penalties and interest, and penalties are usually lower for a voluntary disclosure.7Source 7HMRC, Tell HMRC if you've claimed too much Research and Development (R&D) tax relief (14 August 2026). Take advice before you use either route: the correcting a claim page sets out what to settle first, including what the engagement letter says about the fee on the corrected amount.

If HMRC checks the claim within the time limits above, it can ask for the evidence behind it. Keep the return and the additional information form as filed, the technical narrative, the cost workings, the time and project records they rest on, and the engagement letter. Ask for anything the adviser holds that you do not (ownership of records and work).

• If your claim is reviewed and complaints about an adviser in the United Kingdom
• Claim reduced on review and if you are charged a penalty
• The true cost of a claim

Sources

1. HMRC, Submit detailed information before you claim Research and Development (R&D) tax relief (26 September 2025); HMRC manual CIRD182000 (25 August 2026).  Back
2. HMRC Compliance Handbook CH81010 (7 October 2026): the penalty is charged on the person who gives the inaccurate document (Finance Act 2007 Schedule 24 paragraph 1).  Back
3. HMRC manual CIRD81800 (25 August 2026), Finance Act 1998 Schedule 18 paragraph 83E.  Back
4. HMRC, Company Tax Returns: making changes.  Back
5. HMRC Enquiry Manual EM1510 (30 September 2026), Finance Act 1998 Schedule 18 paragraph 24.  Back
6. HMRC Compliance Handbook CH51300 and CH56200 (7 October 2026), Finance Act 1998 Schedule 18 paragraph 46.  Back
7. HMRC, Tell HMRC if you've claimed too much Research and Development (R&D) tax relief (14 August 2026).   Back
8. HMRC, Compliance checks: penalties for inaccuracies in returns or documents, CC/FS7a (21 July 2026).  Back
9. HMRC Compliance Handbook CH81166 (7 October 2026), Finance Act 2007 Schedule 24 paragraph 1A.  Back