The issue affects up to 4,500 taxpayers signed up to the MTD trial and HMRC wrote to them before the self assessment payment deadline of 31 January, advising them about the issue and giving them instructions on how they can address the problem.

ICAEW first raised the problem after being told by HMRC there was a problem affecting taxpayers who have signed up to the MTD trial and are required to make payments on account for the 2025-26 tax year.