A compliance check is HMRC's formal name for what most people call an enquiry. It's a procedural step, not an accusation, and a meaningful share close with the claim accepted as filed or with minor adjustment. That said, it isn't nothing either. It changes the timeline, usually means the money doesn't arrive when you expected, and how the response is put together matters.
Why this claim, specifically
What tends to draw scrutiny
As covered on R&D Tax Relief, the claims that draw scrutiny are rarely the ambitious ones. They're the thin ones. A technical narrative that could describe almost any project, rather than the specific uncertainty this company actually faced, is a bigger red flag than a genuinely difficult but well-documented claim. If your Additional Information Form leaned on general description rather than specifics, that's often where an enquiry starts.
HMRC's own published figures show compliance checks have become considerably more common: coverage rose from 10% of claims received in 2022-23 to 17% in 2023-24 (see HMRC's published approach to R&D tax reliefs, 2023 to 2024). Being selected isn't the rare event it once was, and it says less about your claim specifically than it would have a few years ago.
What HMRC typically asks for
Correspondence, not a phone call out of nowhere
An enquiry usually opens with a letter, and it usually asks for something concrete: further detail on the technical narrative already submitted with the Additional Information Form (see what that form actually requires), evidence supporting the cost breakdown, or clarification of who did the work and how the uncertainty was resolved. The letter will set out what's being asked and a window to respond in. Missing that window, or responding vaguely, tends to prolong the check rather than close it.
Worth being direct about: going quiet doesn't make an enquiry go away. HMRC correspondence left unanswered doesn't default in the company's favour. It tends to escalate, and a claim can end up formally amended or removed by HMRC if nobody responds. Whatever else is true, this is the one thing worth acting on immediately.
The realistic timeline
Enquiries generally run longer than people expect
There's no single fixed length. It depends on the complexity of the claim and how quickly information moves between the company, any adviser involved, and HMRC. In practice these can run for a number of months, sometimes longer where correspondence goes back and forth more than once. If a lender is being asked to advance against the claim while an enquiry is open, that timeline matters there too (see R&D advance funding for how an open enquiry generally changes what's on offer rather than ruling it out).
Responding yourself, or bringing someone in
Where specialist input actually earns its place
Not every enquiry needs a specialist adviser parachuted in. A straightforward request for clarification on a point already well documented can often be answered directly. Where it tends to matter more is when the request goes to the substance of the technical narrative itself (whether the work genuinely met the uncertainty bar), because that's a different skill to preparing the original claim and not every adviser who prepares claims also handles enquiry defence well. It's worth checking this specifically before instructing anyone: our adviser register records what each firm states about enquiry defence, where they publish anything at all.
Decision helper
Alternatives and limitations
If your original adviser has stopped responding while this is live, that's a separate and common problem: see an adviser gone quiet mid-claim. And if the enquiry has already concluded with the claim reduced or refused, this page is now behind you. See what a rejected or reduced claim actually means for what comes next.
