The First 7 Days After an HMRC R&D Enquiry Letter
Greyledger — free edition. Verified against the legislation, HMRC manuals and tribunal decisions as at July 2026. This is information, not advice; nothing here is sent to HMRC by us.
An enquiry letter is designed to feel like a deadline with a threat attached. Most of what determines the outcome, though, is decided in the first week — before anything is sent. These are the seven things worth doing, in order.
Day 1 — Check the enquiry is actually valid
HMRC may only open an enquiry within a statutory window (Finance Act 1998, Schedule 18, paragraph 24). For most SME claimants the window is 12 months from the date your return was delivered to HMRC — the date you filed, which is earlier than the statutory deadline if you filed early. For late or amended returns the window runs to the quarter-end following the first anniversary of delivery or amendment.
Find the filing date, find the date on the enquiry notice, and count. A notice given outside the window is not a valid enquiry, and responding substantively to an invalid notice can waive the point. If it is close, take advice before engaging at all.
Day 1–2 — Acknowledge, and ask for more time in writing
The 30 days on the letter is administrative, not statutory. HMRC's own Enquiry Manual (EM1580) treats it as a minimum guideline and requires officers to allow longer where warranted. No penalty attaches to an informal request; formal information notices under Schedule 36 FA 2008 (with their £300 and £60-a-day penalties) come later, and only if you stonewall.
Write back now: confirm receipt, and request a realistic extension with a reason — 8 to 12 weeks is a normal ask for an R&D enquiry. Keep the request and the reply. This costs nothing and cannot be held against you.
Day 1–3 — Pull your Additional Information Form and reconcile everything to it
Every claim filed since 8 August 2023 required an Additional Information Form, and it is the version of your claim HMRC is looking at. Your enquiry response must be consistent with it: project descriptions, expenditure categories, intensity figures. A response that quietly tells a different story from the AIF is read as a credibility failure, whatever its merits.
Get the AIF, the CT600, the accounts and any adviser workings side by side before forming a view on anything.
Day 2–4 — Find your competent professional, and confirm they will stand up
The single most common reason R&D claims fail at tribunal is not the technology — it is the witness. In Flame Tree Publishing (2024) the claim failed because no witness was qualified in the specific technical field. In Beer Express (2026), over £490,000 was disallowed with a credible business owner testifying, because the person who actually did the technical work was retired abroad and never called. Against that, Get Onbord (2024) succeeded with a director who had no formal qualifications but deep, current expertise: qualifications are not the test, real expertise is.
Identify who did the technical work. Can they explain the state of knowledge in the field when the project started, the specific uncertainty they faced, and why a peer could not readily have resolved it? If that person has left, is abroad, or is unavailable, that is your most urgent problem — ahead of any drafting.
Day 2–5 — Preserve the contemporaneous record, untouched
Gather what exists as it exists: code repositories with commit histories, meeting notes, lab notebooks, project plans, internal emails, timesheets. Do not tidy, summarise or reorganise anything yet. HMRC's practice note (CIRD80520, applying the BE Studios standard) expects claims to rest on contemporaneous documentation; retrospective spreadsheets presented as if contemporaneous have sunk cases (Tills Plus, 2024).
Day 3–5 — Understand your penalty exposure before choosing your posture
Penalties for inaccuracies run under Schedule 24 FA 2007: careless up to 30%, deliberate up to 70%, deliberate and concealed up to 100% of the potential lost revenue. Two things people learn too late: once the enquiry letter has arrived, any disclosure is "prompted", so the floor for a careless inaccuracy is 15%, not nil; and careless penalties can be suspended for up to two years with conditions — deliberate ones cannot. Since 2024 HMRC can also withhold payment of a payable R&D credit while the enquiry is open, so the cash-flow assumption behind your claim may already be gone.
Quantify the worst case first. It changes how you weigh concession against defence, calmly rather than under pressure.
Day 1 (and before instructing anyone) — Check who is allowed to speak for you
Since 18 May 2026, an adviser who interacts with HMRC on your behalf must be registered with HMRC under the Finance Act 2026 regime. If you instruct someone to correspond, call or file for you, check their registration and your 64-8 authorisation. If you respond in your own name — with help behind the scenes — no agent registration or 64-8 is involved, and everything HMRC receives is something you have read and signed. Be wary of a second wave of contingency-fee "enquiry defence" firms charging a percentage; the incentive structure that produced many of these enquiries is not the one to hire for the response.
What HMRC is actually testing
Underneath every question in the letter sit four concepts from the DSIT guidelines (the statutory definition of R&D, current version as amended March 2023):
- Advance — in the overall knowledge of the field, not just your company's knowledge.
- Uncertainty — whether something is scientifically or technologically feasible, or how to achieve it in practice; commercial risk does not count.
- Competent professional — the benchmark person against whom "readily deducible" is measured.
- Baseline — what was publicly known or readily deducible when the project began.
A response that answers the letter's questions without anchoring each project to those four concepts, with evidence, is a response that extends the enquiry rather than closing it. Enquiries end by closure notice (Sch 18 para 32); if positions harden, there is statutory review (TMA 1970 ss.49A–49I), alternative dispute resolution, and the First-tier Tribunal — in that order of cost.
Prepared by Greyledger. If you want the full response pack — analysis, strategy, technical narrative, cost reconciliation and a response letter for your own signature — the fixed fee is £499, £199 deposit to start: https://greyledger.co.uk/rd-enquiry