HMRC R&D Nudge Letter: Response Playbook (Step-by-Step)

An HMRC R&D nudge letter is a one-to-many communication sent under HMRC's compliance strategy. It is used as part of the R&D tax relief reform programme set out in the government's R&D tax reliefs collection. Nudge letters were sent in volume from 2023 onwards as HMRC sought to reduce the estimated £4.1bn in error identified in R&D claims. The key fact: receiving a nudge letter is not the same as being under formal enquiry. But how you respond matters for your legal position. Use our eligibility checker to assess your claim position before drafting a reply.

What a Nudge Letter Is (and Is Not)

A nudge letter is sometimes called a "one-to-many" communication. HMRC identifies a group of claimants with similar risk characteristics, for example software companies with first-year R&D claims above a certain threshold, or construction firms with subcontractor costs, and sends the same letter to the entire group. The letter is not based on a review of the individual company's claim. HMRC has not examined your specific records.

A nudge letter is not a formal compliance check opened under section 9A of the Taxes Management Act 1970. It does not create a statutory obligation to respond. It does not stop you from amending your return voluntarily. It does, however, affect how HMRC treats the situation if an error is subsequently found: any amendment made after receiving a nudge letter counts as a "prompted disclosure" under Schedule 24 of the Finance Act 2007, which reduces the maximum penalty mitigation available compared to a genuinely unprompted disclosure.

HMRC's approach to nudge letters is described in its compliance handbook. For the formal enquiry process that may follow, see the HMRC enquiries pillar page.

The Four Nudge Letter Formats HMRC Uses

HMRC has used different nudge letter formats across its various R&D compliance campaigns. The four formats below reflect the versions in circulation from 2023 to 2026. Each places different demands on the recipient.

Format 1: General Sector Letter

The broadest format. HMRC identifies that your company is in a sector with high rates of R&D non-compliance and writes to all companies in that sector that have made R&D claims in recent years. The letter typically says HMRC has seen high error rates in claims from companies like yours, lists the main risk areas (qualifying activities, apportionment, subcontractors), and asks the company to review its claim. No specific issues with the company's own claim are identified.

The appropriate response to a Format 1 letter is a written confirmation that you have reviewed the claim and believe it to be correct, with a short explanation of why. If the review reveals issues, a prompted amendment is the correct course.

Format 2: Specific Issue Letter

This format names specific concerns about the company's claim. Common examples include: "We note your claim includes costs for overseas subcontractors; please confirm these meet the UK provision requirement" or "We note your claim includes 100% staff apportionment; please confirm this is accurate." This version is targeted, not generic, and suggests that HMRC has done at least a basic review of the company's AIF or CT600 before sending the letter.

A Format 2 letter requires a direct written response to the specific point raised. Ignoring it substantially increases the probability of HMRC converting the nudge into a formal compliance check.

Format 3: Pre-Repayment Check

Sent before HMRC processes a repayment claim for a loss-making company. HMRC uses this format to pause the repayment while it gathers information to satisfy itself that the claim is correct. This is the most time-sensitive format; the repayment will not be made until the check is resolved. The letter usually asks for the technical narrative and cost reconciliation to be supplied within 30 days.

This is functionally a compliance check, even though it may use nudge-style language. Treat it as a formal enquiry opening and respond with a full information package.

Format 4: Post-Amendment Review

Sent after a company has already amended its R&D claim, either voluntarily or after a prior nudge. HMRC uses this format to confirm that the amendment is complete and that no further issues exist. It may ask for a short confirmation in writing, or it may ask for the working papers behind the amended claim. The risk is that this format can be a precursor to a formal compliance check if HMRC is not satisfied with the amendment.

What Not to Do When You Receive a Nudge Letter

Three common mistakes make the situation worse:

Do Not Withdraw Automatically

The most damaging mistake. Many companies receiving nudge letters immediately instruct their accountant to withdraw the claim to avoid any further contact from HMRC. If the claim was correct, this gives up legitimate tax relief, potentially tens or hundreds of thousands of pounds. The nudge letter does not indicate that HMRC has evidence that the claim is wrong; it indicates that your company profile matched a group HMRC decided to contact.

Do Not Ignore It

While there is no legal obligation to respond to a Format 1 nudge letter, failing to respond to a specific-issue letter (Format 2) or a pre-repayment check (Format 3) will make things worse. For Format 3 letters, the repayment is held until HMRC receives a satisfactory response. For all formats, ignoring the letter removes the option of a prompted voluntary disclosure if you later find an error, and may result in HMRC opening a formal enquiry.

Do Not Overcorrect

Some companies, after receiving a nudge letter, become so risk-averse that they strip legitimate costs out of the claim or apply excessively conservative apportionment percentages. This is unnecessary. The correct response is to test the claim against the actual rules, not to apply an arbitrary haircut to reduce the amount in case of future scrutiny.

How to Respond If You Are Confident in the Claim

If your R&D claim was prepared by a specialist adviser with proper technical narratives, contemporaneous time records, and a defensible apportionment methodology, the response to a nudge letter is relatively straightforward.

Write to HMRC at the address on the letter (or via the online portal if one is specified). Include:

• A confirmation that you have reviewed the claim in response to HMRC's letter.
• A brief statement of why you believe the claim is correct, addressing any specific issues raised in the letter.
• A short technical summary of the qualifying projects, if not already on file in the Additional Information Form.
• Contact details for the specialist adviser who can respond to any follow-up questions.

Do not send every piece of supporting documentation unprompted; if HMRC wants more, it will ask for it via a formal information notice. Sending a large volume of unsolicited documents can extend the review and raise new questions.

How to Engage If You Are Not Confident in the Claim

If the claim was prepared by a firm you are no longer working with, or if the original preparation was rushed, the nudge letter is an opportunity to get a second opinion before HMRC escalates.

The process should be:

1. Obtain the original working papers from the firm that prepared the claim. If they are unavailable, reconstruct what you can from payroll, project management systems, and finance records.
2. Commission a technical review from an HMRC-registered specialist. This review should test the qualifying activities description against the BIS Guidelines at gov.uk, and verify the cost categorisation against CIRD83000.
3. If the review finds errors, prepare an amended return and file it with a covering letter explaining the amendment. Filing a prompted amendment before HMRC formally opens a compliance check reduces the penalty exposure.
4. If the review finds the claim is correct, write to HMRC confirming your position.

For definitions of the qualifying activities test and the competent professional standard, see the R&D tax glossary.

Deadlines and Time Limits

The nudge letter itself typically asks for a response within 30 days. This is not a statutory deadline, but it is the timeframe HMRC expects. If you need more time, write to acknowledge receipt and request an extension; most HMRC officers will grant 2 to 4 additional weeks without difficulty.

The statutory time limit for amending a CT600 is 12 months from the filing deadline for the period in question, per section 83 of the Finance Act 1998. If that window has passed, any correction must be made by HMRC or through a claim for overpayment relief under Schedule 1AB of the Taxes Management Act 1970. A specialist adviser can advise on the correct mechanism.

HMRC's own time limits for opening a compliance check are 12 months from the filing date for a standard return, four years for careless errors, and six years for deliberate inaccuracies. The nudge letter does not toll these limits; they run regardless.

Penalty Mitigation: Prompted vs Unprompted Disclosure

Under Schedule 24 of the Finance Act 2007, the penalty regime for inaccuracies in returns distinguishes between unprompted and prompted disclosures. An unprompted disclosure is one made before HMRC has started any enquiry or audit activity. A prompted disclosure is one made after HMRC has indicated it is going to review the matter.

HMRC's position, which has been confirmed in tribunal cases, is that a nudge letter counts as HMRC indicating it is reviewing R&D claims in the relevant sector. An amendment made after receiving a nudge letter is therefore a prompted disclosure, not an unprompted one. The practical effect is that penalty mitigation is lower, but still materially better than waiting for HMRC to make the correction after a formal enquiry.

When a Nudge Letter Escalates to a Formal Enquiry

HMRC may open a formal compliance check after a nudge letter in three situations: the company does not respond at all, the company's written response raises further questions, or the campaign that generated the letter is designed to transition selected cases to formal enquiry regardless of the response.

If a formal enquiry is opened, the HMRC enquiries guide sets out the process, information requests, and response strategy. The week-by-week timeline covers the typical sequence from letter receipt to closure. If the enquiry results in an amendment notice you disagree with, the when-to-appeal guide sets out the options.