How Long Should an HMRC R&D Enquiry Take? Service Standards Explained

HMRC opened approximately 9,700 R&D compliance checks in 2023-24 according to HMRC's Annual Report. Some close in three months; others run for three years. Understanding what determines timeline and what rights you have when an enquiry drags is essential for any company under active HMRC review. The HMRC enquiries guide covers the overall process; this post focuses specifically on timeline standards and how to enforce them.

What HMRC Actually Publishes on Timelines

HMRC's general correspondence standard, set out in the HMRC service standards, commits to responding to written correspondence within 15 working days. For telephone calls, the target is to answer within five minutes.

These standards apply to individual correspondence items within an enquiry, not to the overall enquiry duration. HMRC publishes no specific commitment on how long an R&D compliance check should take from opening to closure notice. This is a gap in accountability that has led to some enquiries running for considerably longer than is reasonable given the underlying facts.

HMRC's Compliance Handbook at CH21000 sets out the principles that enquiries should be handled professionally, proportionately, and without unnecessary delay. These principles give grounds for complaint but are not an enforceable timeline commitment.

Typical Timelines in Practice

Based on sector experience, R&D enquiries in 2024-2025 have followed broadly these patterns:

• Simple enquiries, straightforward response: 3 to 6 months from opening to closure notice where the taxpayer responds fully to information notices and the claim can be substantiated on the evidence.
• Contested technical position: 9 to 18 months where HMRC and the taxpayer disagree on whether activities meet the technical uncertainty test and correspondence goes through multiple rounds.
• Complex cases involving multiple periods or connected parties: 18 to 36 months in some instances, particularly where HMRC has taken specialist external advice or where parallel investigations are running.

The most reliable predictor of enquiry length is not the complexity of the facts but the quality of the initial response to HMRC's information notice. A complete, well-organised response to the first notice that addresses every question raised is far more likely to lead to a quick closure than a piecemeal response that generates follow-up questions.

Your Right to Apply for a Closure Direction

Section 28A Taxes Management Act 1970 gives the taxpayer the right to apply to the First-tier Tax Tribunal for a direction requiring HMRC to close the enquiry within a specified period. The tribunal can make this direction where it is satisfied that HMRC has had a reasonable opportunity to conduct its enquiries.

This is a formal legal process. The tribunal considers whether HMRC has been given enough time relative to the complexity of the case and whether there is a legitimate reason for continued delay. It is not a rubber stamp, but courts have been willing to make closure directions where HMRC cannot point to specific outstanding work that justifies the continued delay.

The practical steps are:

1. Write to HMRC and ask them to confirm what specific information or steps remain outstanding before they can close the enquiry.
2. If HMRC cannot give a clear answer or gives a vague one, make a formal complaint through HMRC's complaints process.
3. If the complaint is not resolved satisfactorily within eight weeks, escalate to the Adjudicator's Office.
4. If the enquiry is still not progressing, apply to the First-tier Tribunal for a Section 28A closure direction.

What Causes Enquiries to Run Long

The most common causes of long enquiries are:

• Incomplete responses to HMRC information notices that generate follow-up questions rather than closing the loop.
• Adviser changes mid-enquiry that create a delay while the new adviser gets up to speed.
• Cases where HMRC refers the technical question to an external scientific adviser, which can add months to the process.
• Enquiries that overlap with wider HMRC investigations into a particular adviser firm.
• Cases where the underlying claim was poorly documented and HMRC has legitimate grounds to press for more information.

Companies and advisers who respond promptly, provide organised documentation, and do not attempt to drip-feed information typically close their enquiries faster. If your enquiry has been open for more than 12 months and you have been responsive throughout, it is worth formally asking HMRC what remains outstanding. See our guide on what to do when a claim is rejected if the enquiry has produced a negative outcome, and our post on what triggers R&D enquiries to understand how selection works.

Interest and Penalties While an Enquiry Is Open

If HMRC has already paid out an RDEC credit and the enquiry subsequently results in a recovery, interest runs on the amount from the date of payment. The interest rate HMRC charges on underpaid tax is set at the Bank of England base rate plus 2.5 percentage points and has been material in recent years given elevated base rates.

Penalties for R&D overclaims depend on the category of inaccuracy. Careless errors attract penalties of 15% to 30% of the understated tax. Deliberate inaccuracies attract 35% to 70% (with disclosure) or 70% to 100% (without disclosure). Where the inaccuracy was introduced by an adviser without the company's knowledge and the company took reasonable care, penalties may be reduced to nil. See our post on adviser liability for more on this.

For a company under enquiry on a genuine claim, the risk is interest and professional costs rather than penalties, provided the claim was prepared in good faith with proper documentation. The lesson is that a well-documented claim with a strong Additional Information Form reduces both enquiry risk and the cost of responding when one occurs.