There is no fixed length. The legislation sets a deadline for opening an enquiry and none for closing one. An enquiry therefore lasts as long as the disagreement does, and that turns on what HMRC is questioning and how quickly the answer can be evidenced. The stages are fixed. The intervals between them are not.
How it opens
With a letter, and only with a letter. Paragraph 24 of Schedule 18 to the Finance Act 1998 lets an officer enquire into a company tax return “if he gives notice to the company of his intention to do so”. Where HMRC withholds payment because it thinks a claim may be incorrect, its published aim is to open an enquiry within 60 days of receiving the claim — the one stage with a target attached.
The middle, where the months go
Rounds. HMRC writes, you answer, documents follow, HMRC writes again. Each round carries two waiting periods, theirs and yours, and the number of rounds, not the size of the claim, fills the calendar. The material itself is on our page on what HMRC asks for.
Where a request goes unanswered, HMRC can formalise it. Schedule 36 to the Finance Act 2008 lets an officer require information or documents by written notice, where reasonably required to check the taxpayer’s tax position. There is a right of appeal against such a notice, though not for statutory records or where the tribunal approved it. Meetings work differently: getting a working engineer and an HMRC officer into the same hour is often the slowest booking in the file.
The routes out
Agreement, then closure. Completion is a notice too: paragraph 32 gives a partial closure notice where one matter is finished, a final closure notice where the enquiry as a whole is. Partial closure matters here — one contested project need not hold the rest of the claim hostage. Paragraph 34 carries the amendments giving effect to HMRC’s conclusions, and an appeal against one runs 30 days from notification. That appeal goes to HMRC first: in BW Interiors Ltd v HMRC one sent straight to the tribunal was struck out.
Where an enquiry has stopped moving, paragraph 33 lets the company ask the tribunal to direct HMRC to close it within a specified period. The tribunal must give that direction unless satisfied the officer has reasonable grounds for not closing.
Alternative Dispute Resolution runs alongside all of it. While an enquiry is open you can apply at any stage, and applying gives up no right to appeal or to ask for a review. An HMRC officer trained in mediation acts as a neutral and impartial mediator who “will not suggest or impose solutions”. Once HMRC has made a decision the order changes: for corporation tax, where a review has been offered, the appeal has to be notified to the tribunal and acknowledged first, and paper and basic cases are excluded — how do I appeal an HMRC decision on an R&D claim? sets that out.
Then the formal track: 30 days from a decision letter to appeal or accept a review; a review officer from another team, uninvolved in the original decision, who upholds, varies or cancels it, usually within 45 days on HMRC’s own account; then 30 days from the review letter to appeal to the First-tier Tribunal, which is independent of HMRC.
What that means in months
From practice rather than published data: a check where the records exist and answer the questions asked can close in weeks. Where HMRC contests whether the work met the definition of R&D, or whether a cost head qualifies, expect months. A case that runs through statutory review to the tribunal is measured in years. No one can hand you a date — not us, and not the officer holding the file. Where an R&D dispute has run all the way to a hearing, what the tribunals have decided on R&D records the outcome and the reasoning.
None of this is unusual now. HMRC checked around one in six claims in 2023-24, its latest published figure.
What shortens an enquiry in practice
Records made while the work was happening, rather than assembled afterwards. First responses that answer the whole question instead of inviting the follow-up. The competent professional taking the technical points directly, because an adviser paraphrasing an engineer produces the answer that needs another letter. Every partial answer buys another round, and rounds are what the calendar is made of. What has to be repaid at the end, if anything, is a separate question.
Where to go next
Our HMRC enquiries guide walks the process stage by stage, and enquiry support is included as standard for claims we prepare. If an enquiry into a claim someone else filed has landed on your desk, HMRC enquiry defence sets out how we take that on as a standalone engagement, and where our role ends. Talk to us — we will give you an honest read on where it stands.
Sources
- FA 1998 Sch 18 para 24 — an enquiry begins with notice of enquiry given to the company.
- FA 1998 Sch 18 para 32, para 33 and para 34 — completion by partial or final closure notice; the company’s right to apply to the tribunal for a direction to close, which the tribunal must give unless the officer has reasonable grounds not to; amendment of the return to give effect to the conclusions, and the 30-day appeal window against that amendment.
- FA 2008 Sch 36 para 1 and para 29 — the power to require information or documents reasonably required for checking a taxpayer’s tax position, and the right of appeal against a taxpayer notice, excluding statutory records and tribunal-approved notices.
- CIRD80525: practice note for ISBC and WMBC — the aim to open an enquiry within 60 days of receiving the claim where HMRC decides not to pay.
- Use alternative dispute resolution to settle a tax dispute and CC/FS21 — availability at any stage while a compliance check is open, and at the end of one where an appealable decision has been made; the mediator as a neutral and impartial HMRC officer who will not suggest or impose solutions; that ADR does not affect the right to appeal or to ask for a review; and that for direct tax, where a review was offered, the appeal must be notified to the tribunal and acknowledged before applying, with paper and basic cases excluded.
- Disagree with a tax decision: appeal against an HMRC decision and get a review — the 30 days to appeal or accept a review, the review officer from a different team, reviews usually taking 45 days, and 30 days from the review result letter to appeal to the tribunal. Tax tribunal — the tribunal’s independence of government and HMRC.
- HMRC’s approach to R&D tax reliefs 2023 to 2024 — 9,700 compliance checks against 61,000 claims received, 17% coverage.
CIRD80525 is indexed on our CIRD reference index, with HMRC’s own title for it, a line on what it says and the date HMRC last revised it.
This page describes the rules as they stood at the review date above, as general information rather than advice on your circumstances. For how that distinction works, see our terms; for an answer on your own facts, talk to us.