- By Dov Paluch | Director, Catalyst Solutions
Submitting an R&D tax claim is not the hard part. The hard part is being able to justify every aspect of it if HMRC decides to look more closely.
Many businesses find out their documentation wasn’t good enough at exactly the wrong moment. When a compliance check has already started, reconstructing records from memory or assembling retrospective summaries is rarely enough. HMRC expects to see evidence created during the R&D process itself, not pulled together afterwards to support a submission.
Understanding what that evidence looks like, and where the gaps tend to appear, starts well before a claim is prepared.
Since April 2023, every R&D tax claim in the UK requires a mandatory Additional Information Form to be submitted to HMRC before or on the same day as the Company Tax Return, or Amended Tax Return, depending on which contains your R&D Tax Relief claim. This is not optional and it is not a formality.
If the tax return is submitted first, the claim is rejected and depending on timing, there may be no opportunity to resubmit within the same accounting period, regardless of how strong the underlying R&D work was.
The form requires the following:
That last requirement is where many businesses struggle. Describing a genuine scientific or technological uncertainty is not the same as describing a technical problem. HMRC’s guidance is clear that a problem is not an uncertainty if it can be resolved in a discussion with peers. The uncertainty must be something that a competent professional working in the relevant field would also find uncertain. Getting this wrong in the AIF does not just weaken a claim, but it can signal to HMRC that the underlying R&D activity may not qualify at all.
The AIF sets the framework but it is not the entirety of what HMRC expects. Behind every claim there should be a body of technical evidence that demonstrates genuine R&D activity took place.
HMRC is asking three questions when it reviews a claim:
The technical evidence needs to answer all three, clearly and consistently.
What that looks like in practice varies by sector. Some examples:
The common thread is that the evidence should tell a coherent story from project inception through to outcome. It should show not just what the company did but why what it was attempting was genuinely uncertain, and what the systematic process of investigation looked like. Failed experiments and abandoned approaches are as relevant as successful ones. They demonstrate that the work involved real uncertainty, not a straightforward application of existing knowledge.
Technical evidence alone is not sufficient. Every pound claimed needs to be supported by financial documentation that accurately apportions costs to qualifying R&D activity.
The point that is most often missed is that the financial evidence and the technical evidence need to tell the same story. If the technical narrative describes a project running from January to September but the staff time records show R&D activity only in Q1, that inconsistency will be visible in a compliance check. The two strands of a claim need to be built together, not in parallel by separate teams who never compare notes.
One of the most significant distinctions HMRC makes is between contemporaneous records and retrospective summaries. A contemporaneous record is created at the time the R&D activity takes place. A retrospective summary is created after the fact, often at claim time, to describe what happened.
Both can be submitted as evidence. Only one carries real weight.
Contemporaneous records show R&D activity in progress. They capture the uncertainties, the failed approaches, the iterative nature of genuine research and development. A retrospective summary, however well written, describes the outcome of a process rather than the process itself. It tends to make R&D look cleaner and more linear than it was, which can paradoxically make it less convincing to a reviewer who understands what genuine innovation looks like.
The practical implication is that documentation cannot be treated as a year-end or even well post year-end exercise. Evidence gathering needs to be built into how R&D projects are run, not added at claim time. That does not mean creating additional administrative burden. It means ensuring that the records a technical team would naturally produce such as project plans, meeting notes, test results, code commits and design iterations, are retained and organised in a way that supports the claim. This often, in fact, makes the technical narrative creation a simpler process.
There is a common assumption that once a claim has been submitted and a payment received, the matter is closed. This is not the case.
HMRC processing a claim and paying out does not mean the claim has been reviewed or validated. The compliance check is a separate process that can follow months or years after the original submission. HMRC has up to 15 months to open an enquiry into an R&D claim in most cases, up to 4 years to open a Discovery Assessment and longer where there is reason to suspect fraud or negligence.
This matters for documentation because the evidence that supports a claim needs to be retained and accessible well beyond the year in which it was submitted. A business that treats documentation as a one-time effort at claim time may find itself unable to respond adequately to an enquiry raised two or three years later.
Understanding what triggers a compliance check in the first place is also relevant here.
The difference between documentation that holds up and documentation that does not is rarely about volume. It is about specificity and coherence.
Weak documentation tends to describe R&D activity in general terms. It names projects without explaining what was genuinely uncertain about them. It lists costs without demonstrating a clear link to qualifying activity. It describes outcomes without showing the process that led to them.
Strong documentation is specific. It identifies the precise scientific or technological uncertainty that existed at the start of each project. It explains why that uncertainty could not be resolved using existing knowledge or standard techniques. It shows the systematic process by which the company sought to resolve it, including the approaches that did not work, and it connects that technical narrative directly to the costs being claimed.
Building documentation to that standard requires input from both the technical and financial sides of a business. The people who understand the science or engineering need to be involved in describing the uncertainty and the process. The people who manage the finances need to ensure that cost records accurately reflect the scope and timing of the R&D activity. Neither can do it adequately without the other.
The requirements described in this article are not new. The Additional Information Form has been mandatory since April 2023. The expectation that R&D claims are supported by contemporaneous technical and financial evidence has always been part of the framework.
What has changed is the level of resource HMRC is committing to checking whether those requirements are being met. HMRC’s R&D compliance team has grown from 100 staff in 2021 to over 500 in 2024. A fivefold increase that has translated directly into more checks, more detailed enquiries, and less tolerance for claims that cannot be properly evidenced. Understanding what draws HMRC’s attention in the first place is worth knowing before you submit.
Getting documentation right is not a one-time exercise. It is built into how a claim is constructed from the start, project by project, cost by cost. For most businesses, doing that well requires working with advisors who understand both the technical and the financial dimensions of what HMRC is looking for and who can identify gaps before a claim is submitted rather than after an enquiry letter arrives.
About the author
Dov Paluch is a director at Catalyst Solutions, a multi-disciplinary R&D tax advisory firm serving innovative businesses across the UK, South Africa, Australia and Germany. The Catalyst Solution’s team includes accountants, lawyers, engineers, and scientists and is built on the belief that the only R&D tax claims worth building are those you can confidently explain years later.
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