Nearly half have already had their claims declared invalid by HMRC since the new documentation requirement came into effect on 8 August 2023.

Companies that have not yet complied with the new forms will soon begin receiving letters from HMRC saying their R&D claim is invalid unless they amend their returns, warned the top 10 firm.

In a recent letter sent to agents, the tax authority stated that almost half of all claims received so far between 8 August and 3 September have been submitted by customers without the required additional information form (AIF).

The AIF is required for claims for both SME R&D tax relief and the R&D expenditure credit (RDEC).