R&D tax relief •8 min read

The Additional Information Form (AIF)

MJ

Matthew Jones ACA CTA

Last reviewed August 2026 · Editorial standards

The Additional Information Form (AIF) is a mandatory online form that carries the substance of your R&D claim to HMRC: the projects, the costs, the responsible people and the agents involved. It has been required for every R&D claim submitted since 8 August 2023, whatever the scheme, and it must reach HMRC before or with the company tax return (CT600). A claim filed without it is not a valid claim.

What is the Additional Information Form?

It is HMRC’s standard template for the detail behind an R&D claim. Before August 2023, supporting reports arrived in whatever format the claimant or agent chose, and some claims arrived with no supporting detail at all. The AIF ended that: every claim now presents its projects and costs in the same structure, and everyone who worked on the claim is named.

Treat it as the claim itself rather than an administrative wrapper. When HMRC looks at your claim, the AIF is normally the first document read, and the impression it creates shapes everything that follows.

What information does the AIF require?

Four things.

Project descriptions. Each described project must show how the work meets the statutory definition of R&D: an advance in a field of science or technology, sought through the resolution of scientific or technological uncertainty that a competent professional in the field could not readily resolve. The advance must belong to the field, not merely to your company. Our guide to what counts as qualifying R&D sets the definition out in full.

Qualifying costs. The expenditure behind the claim, broken down by category: staffing, externally provided workers, subcontractors, consumables, software, data and cloud computing, and payments to clinical trial volunteers. The figures need to reconcile with the claim in the return; the categories themselves are covered in which costs qualify for R&D tax relief.

The senior internal R&D contact. A named senior person at the claimant company who is connected to the R&D. This should be someone who can genuinely speak to the work, because HMRC’s questions will be directed here.

Every agent. Each agent involved in the claim must be named. Anonymous advisers are no longer possible, which was part of the point: some unregulated agents built businesses on never appearing in the paperwork. HMRC registration for tax advisers who interact with HMRC is required as well, phased in from 18 August 2026, so the naming requirement has real teeth. It also gives claimants a simple due diligence question: ask any prospective adviser whether they are registered with HMRC and whether their name will appear on your form.

When must the AIF be submitted?

Before or with the CT600, never after. Sequencing is the simplest thing to get wrong: if the return goes in first and the AIF has not been submitted, the claim is defective. Where one adviser prepares the claim and another files the return, someone has to own the sequence. In our engagements that is us: we are registered with HMRC as tax agents and submit both the AIF and the return ourselves, so the sequence does not depend on a handover between advisers.

The requirement applies to every claim, including claims added to earlier returns by amendment. A backdated claim submitted today needs an AIF just as a current-year claim does, and the same sequencing rule applies to the amended return. Companies revisiting older periods should settle the notification position at the same time: the two requirements operate independently, and failing either one is fatal to the claim.

What a completed AIF looks like

HMRC publishes no downloadable template, no PDF and no specimen. The AIF is an online service, reached through the Government Gateway or an agent services account, and it cannot be reopened once submitted — HMRC’s guidance tells you to save a copy first. Draft elsewhere, then transcribe.

The service asks for company details (Unique Taxpayer Reference, employer PAYE reference number, VAT registration number, business type or SIC code); contact details, meaning the main senior internal R&D contact responsible for the claim and every agent involved, defined widely enough to catch anyone who advised, analysed costs or helped prepare the technical assessment; the accounting period start and end date, which must match the dates shown in the Company Tax Return; R&D intensity and connected companies where those apply; qualifying R&D expenditure, including the PAYE cap questions and the costs incurred on qualifying indirect activities; then project details, and describing each project — six substantive fields, plus an optional further-information field, repeated for each project described.

What follows is a worked illustration, not a real claim: Example Coatings Ltd and everyone in it are invented, and the figures are round numbers chosen to hang together. The company claims for two projects, so under the one-to-three rule both are described. This is the larger.

The main field of science or technology. Polymer chemistry, specifically the formulation and curing of water-based barrier coatings for flexible food packaging film.

The baseline level of science or technology that the company planned to advance. Published water-based barrier dispersions reach useful oxygen barrier only above roughly 4 g/m², and lose most of it once the film is creased: the barrier layer microfractures at the fold. Solvent-based systems hold barrier through creasing at a third of that coat weight. Our own prior formulations sat at the same limit as the published work, which is why they are recorded — as evidence of where the field stops, not where we started.

The advance in scientific or technological knowledge that the company aims to achieve. A water-based coating chemistry that retains oxygen barrier after repeated flexing at solvent-system coat weights — an appreciable improvement in what the field can do with water-based dispersions, not merely a formulation new to this company.

The scientific or technological uncertainties that the company faced. Two, both open to the industry rather than to us alone. First, whether the crosslink density needed for oxygen barrier can coexist with the chain mobility needed to survive creasing, or whether the two are inherently opposed in a waterborne dispersion: no published work resolves it and no model predicts it from formulation. Second, whether a barrier surviving flexing at laboratory scale survives the shear and drying profile of a production coater. Our Head of Formulation, Dr H. Prosser — doctorate in polymer science, eighteen years in barrier coatings — could answer neither from existing knowledge. The commercial constraints, target price and running on the customer’s existing converting line, are real and are not uncertainties. They appear nowhere in this field.

How your project seeks to overcome these uncertainties. Four crosslinker chemistries were tested against a structured matrix of loading and cure temperature, each formulation measured for oxygen transmission rate before and after standardised flex testing. Two were eliminated in the first round; a third passed at laboratory scale and failed at pilot-line shear, which itself narrowed the second uncertainty. The fourth went into three pilot trials at progressively lower coat weights. At the period end the first uncertainty is partly resolved and the second is not, so the project continues. Of the project’s qualifying costs, £9,000 relates to qualifying indirect activities — recorded here, against this field, per HMRC’s instruction.

The tax relief you’re claiming and the amount. Merged R&D expenditure credit. Qualifying expenditure attributable to this project, £256,000: staffing £180,000, externally provided workers £42,000, consumable items £28,000, software, data licences and cloud computing £6,000. The second project accounts for the remaining £54,000 of the £310,000 claimed for the period.

Read that against the four elements of qualifying R&D and the pattern is plain: the advance measured against the field’s frontier rather than the company’s, the uncertainty put as a technical question with a reason it could not simply be looked up, the commercial pressures named and then set aside, the work reporting what failed as readily as what worked. The form gives the competent professional no field of her own — HMRC invites those details into the optional separate R&D report. None of that is length. The six answers run to about 430 words.

Where do AIFs go wrong?

Five patterns account for most of the failures we see:

  • The CT600 is filed before the AIF, so the claim fails on sequence alone.
  • Project descriptions read as marketing: they describe a product and its commercial promise rather than the advance in the field and the uncertainties resolved.
  • Project boundaries are drawn around whole development programmes, sweeping routine work into the claim alongside the genuine R&D.
  • The cost figures do not reconcile to the return, or apportionments have no visible basis.
  • The named contact cannot speak to the technical detail when HMRC follows up.

Each of these is avoidable, and each is the sort of signal that invites a full HMRC enquiry — HMRC checked around one in six claims in 2023-24, its latest published figure. We collect the wider set in the common mistakes we see in R&D claims.

How do we prepare the AIF?

From the technical work upwards. That means interviews with your competent professionals, project descriptions written against the statutory definition rather than adapted from marketing copy, and cost workings reconciled line by line before anything is submitted. The same discipline runs through preparing a robust R&D claim. The named senior contact reviews the full draft before it goes to HMRC: follow-up questions land with that person, and the worst time to read your own project descriptions for the first time is during an enquiry. Every claim is prepared by our specialist team and signed off by a chartered adviser, and every AIF we file names us as agent, as the rules require and as we would want anyway: we stand behind our work, and enquiry support is included in every engagement as standard.

The AIF is one of three procedural steps that decide whether a claim exists at all. The others are the claim notification requirement for first-time claimants and the CT600 itself. Which rules apply to your period depends on your accounting dates, covered in which R&D scheme applies to your company.

Talk it through with a chartered adviser

If you want your next AIF prepared by a regulated chartered firm, or a second pair of eyes on one already drafted, get in touch. For the wider claim process, start with our R&D tax relief guide.

Sources