Four things, in essence: descriptions of the R&D projects, a breakdown of the qualifying costs, the name of the senior internal contact responsible for the R&D, and the details of every agent involved in the claim. The Additional Information Form has been mandatory for every R&D claim made since 8 August 2023 — the trigger is the date the claim is made, not the accounting period, so a backdated claim filed now needs one, and a claim made by amendment needs its own. It must be submitted before or with the CT600 that contains the claim.
What each part has to do
The project descriptions carry the technical case. For each described project the form requires the field of science or technology, the baseline knowledge the project set out to improve on, the advance sought, the scientific or technological uncertainties, and how the project sought to overcome them — and HMRC’s guidance on the uncertainties question expects you to explain why the answer was not readily available or deducible by a competent professional in the field. Coverage depends on project count: with one to three projects, describe them all; with four or more, describe at least three that together account for at least half the qualifying expenditure; and where reaching half would take more than ten, describe the ten largest. The cost breakdown allocates the qualifying spend across the statutory categories — staffing costs, software, data licences, cloud computing, consumable items, externally provided workers, payments to the subjects of clinical trials and the qualifying element of contractor payments — and it needs to reconcile to the figures in the return. The category list was tightened in October 2024, when software and consumables were split into separate heads, so a claim prepared on an older template needs re-mapping before the form is drafted.
The two naming requirements are the quiet compliance teeth. The senior internal contact puts a named individual at the company behind the claim, and the agent details put every adviser who worked on it on the record. Both exist because HMRC wants accountability for what is filed, and both mean the form is a poor place for anything anyone involved would not stand behind.
What happens without it, and what a thin one costs
A claim filed without the AIF is invalid: HMRC treats it as not validly made, writes to the company confirming the claim’s removal from the return, and no relief is processed until a compliant form is in — and where that happens close to the amendment deadline, the chance to claim at all can go with it. That is mechanical. The subtler risk is a form that exists but says little, because the AIF is the first thing HMRC reads when it decides which claims to look at, and HMRC checked around one in six claims in 2023-24, its latest published figure. A thin or generic AIF invites the enquiry it could have prevented — and HMRC is explicit that cross-referring to a report outside the form is not an answer, even where HMRC already holds it. A precise AIF, written from real technical input and reconciled cost workings, is the claim’s first line of defence. This is why we prepare it as the core of the claim rather than a form filled in at the end.
Where to go next
Our AIF guide explains what a well-prepared form contains section by section, and where forms go wrong. If a claim was filed for you and you have never seen the AIF that accompanied it, ask for a copy: it tells you a great deal about the standard of the work, and a free claim review will tell you the rest.
Written by Matthew Jones ACA CTA. Last reviewed July 2026.
Sources
- Submit detailed information before you claim — the AIF requirements in full.
- SI 2023/813, Schedule 2 — the statutory information requirements, as substituted from 2 October 2024 by SI 2024/950.
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.