What happens in an HMRC R&D enquiry
HMRC now checks far more R&D claims than it used to - 17% of claims in 2023-24, by its own account, up from 10% the year before. An enquiry isn't an accusation; it's a request to substantiate what you claimed. Here's what the letter asks for, and why the record you already created matters more than anything written afterwards.
The compliance check letter
An informal request, on a clock
An enquiry opens with a letter asking questions about the claim and requesting records. It normally gives at least around 30 days to respond - an informal, extendable request rather than a fixed statutory deadline. Your accountant or agent manages the correspondence.
The first response carries the weight
The quality of the first response matters most. A complete, well-evidenced answer can resolve the check early; a thin one invites rounds of follow-up questions. That is why the evidence needs to exist before the letter does.
What HMRC typically asks for
A technical report
The advance sought, the scientific or technological uncertainties, and how you worked to resolve them - per project.
Cost breakdown by project and category
Qualifying expenditure split by project and by cost category, reconciling to the figures claimed.
Staff-time apportionment
How you decided what share of each person's time counted as R&D - the workings, not just the percentages.
A competent-professional statement
Why a competent professional in the field regarded the uncertainties as genuine - who that person is and what they assessed.
Contemporaneous records
Project plans, technical notes, test logs, version-control records and ticket or email threads created at the time of the work.
Reconstruction is weak. Your git history isn’t.
Written after the letter
Most claims are written up months or years after the work, from memory and a workshop. When the enquiry letter arrives, teams scramble to reconstruct what happened - and a narrative assembled under pressure, with no records behind it, is exactly what HMRC probes hardest.
Written while it happened
Your commits, pull requests and tickets are contemporaneous records - created at the time, timestamped, and attributable. Version-control records and ticket threads are on HMRC’s own list of what an enquiry requests. Aven wires each narrative statement to the record that evidences it, read-only, without ever storing your source code.
How an evidence pack helps - and where Aven stops
When your adviser responds to HMRC, they need the technical report, the cost workings and the underlying records in one coherent, cross-referenced bundle. That is what an Aven evidence pack is: AIF-aligned narratives with a linked commit, PR and ticket trail and a conservative cost model, assembled while the work is still fresh - built to withstand an enquiry, so your adviser isn’t starting from a shoebox.
The boundary, plainly:Aven does not represent you in an enquiry, correspond with HMRC, or provide tax advice. Your accountant or R&D tax agent handles the response and the strategy. Aven’s job is making sure the evidence they respond with already exists.
Common questions
Does an enquiry mean HMRC thinks my claim is fraudulent?
No. A compliance check is HMRC verifying that a claim meets the rules before or after paying it. HMRC has significantly increased how many R&D claims it checks - it reported checking 17% of claims in 2023-24, up from 10% the year before - so well-founded claims get checked too. What matters is being able to substantiate what you claimed.
How long do I have to respond?
The opening letter normally gives at least around 30 days. It's an informal request and the deadline is extendable by agreement, but the quality of your first response matters most, so use the time to respond well rather than fast.
Will Aven handle the enquiry for me?
No. Aven does not represent you in an enquiry and does not provide tax advice. Your accountant or R&D tax agent handles the response to HMRC. What Aven provides is the evidence pack they respond with - narratives with a linked, contemporaneous record behind every statement.
What counts as a contemporaneous record?
Anything created at the time the work happened: commit messages, pull requests, tickets, technical notes, test logs, project plans. Documents written after HMRC's letter arrives are reconstruction, and carry much less weight.
Aven assembles R&D evidence packs for accountant review; Aven Reviewed adds expert review. Aven does not file with HMRC, determine your liability, select your scheme (merged vs ERIS), sequence loss relief, or guarantee any amount - those are your accountant or R&D tax firm's responsibility. Figures are indicative and conservative. Nothing here is tax advice. UK only.
The best time to build the evidence is before the letter.
The Eligibility & Readiness assessment is free, takes a few minutes, and tells you honestly whether Aven is the right fit.
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