One Tax Return Mistake Could Trigger Hefty HMRC Fines Under New Rules: Millions at Risk

Failing to fix a known tax return error could be treated as deliberate, pushing any HMRC penalty into a higher band. (Credit: AI-generated illustration: Google Gemini)

More than 12 million people file a Self Assessment tax return in Britain each year, and a single uncorrected mistake on one of them could soon be treated as a deliberate act by HM Revenue and Customs (HMRC).

Draft legislation published by HMRC on 13 July sets out a new legal 'duty to correct' errors in tax documents, together with a power for the department to issue what it calls a Customer Correction Notice. The measure sits within the Finance Bill 2026-27 and forms part of a wider plan to modernise how tax mistakes are put right.