HMRC has reported that nearly 50% of recent R&D claims risk being invalid because of a failure to include a form that has been mandatory since 8 August 2023. HMRC is writing to companies and their agents to advise them to resubmit tax returns with the form required. Larger companies in the RDEC scheme have been advised to follow HMRC's guidance on how to correct an error shown by a software glitch. The rules on tax deductions and tax credits for research and development expenditure are the subject of change and it is important that companies stay on top of the administrative changes to maximise the availability of them.