The mandatory Research & Development Additional Information Form (AIF) has become the primary screening tool for HMRC and a critical point of failure for some claimants. Erros on the form or difference between the AIF and data in the CT600 tax return form can lead to immediate rejection of claims. In this article and summary video we highlight the top five causes of critical failure linked to the AIF.
HMRC designed the AIF to gather comprehensive, structured data about your R&D projects upfront. It serves as a digital "R&D report" that HMRC's systems directly ingest and compare against your CT600 submission. Any mismatch can be interpreted as a failure to submit a valid claim.
Incorrect Submission Order: The AIF must be submitted to HMRC before or on the same day as your CT600 tax return. If the CT600 arrives first, HMRC's system will automatically reject the R&D claim within that return, even if the AIF is submitted the very next day.
Mismatched Financial Figures: The total qualifying expenditure entered in the AIF must exactly match the R&D figures declared in the relevant boxes of your CT600 tax return form (e.g., Box 660 for SME relief, Box 655 for RDEC, or Boxes 670/675/680 on the CT600L supplementary form). Even minor rounding differences can trigger an automated rejection.
Inconsistent Company Details: Your Unique Taxpayer Reference (UTR), accounting period start and end dates, and company name must be identical across both the AIF and the CT600 and your payroll reference also needs to be correct. Any slight variation or tying errors, will prevent HMRC's systems from linking the two submissions, leading to rejection.
Failure to Tick the Correct Box on the CT600: Box 657 on the CT600 must be ticked to confirm that an AIF has been submitted. Forgetting this simple tick, even if the AIF has been correctly filed, can result in the R&D claim being removed from the CT600.
Missing or Incomplete AIF: Simply put, if no AIF is submitted at all, or if it's substantially incomplete, HMRC will consider the R&D claim invalid and remove it from your tax return.
When a claim is rejected due to these types of errors, HMRC will typically send a letter confirming that the R&D claim has been removed from your Company Tax Return. This can take up to a month or even longer.
This isn't an "enquiry" in the traditional sense, it's an outright rejection of the claim's validity from a procedural standpoint. The immediate consequence is that you lose the benefit of the R&D tax relief or tax credit. Depending on how close you are to the filing deadline or the amendment window (which is typically 12 months after the filing deadline for your tax return), you may have a very limited time to correct the error and resubmit a valid claim. If the deadline has passed, you will completely lose your entitlement to the relief for that accounting period. This makes it very important not to delay doing an R&D claim until close to the two year deadline.