HMRC consults on mandatory XBRL tagging for UK corporation tax returns
On 10 March, HM Revenue & Customs (HMRC) launched a public consultation on changes to company tax returns, with more XBRL data tagging at its heart. The consultation, which runs until 2 June 2026, seeks views from software developers, tax advisers, corporates and representative bodies on implementation timelines and enforcement mechanisms for the new requirements.
The proposals would introduce a fully prescribed format for Corporation Tax computations (the detailed workings submitted alongside the CT600 and company accounts), replacing the current free-format structure. HMRC notes that excessive variation in how XBRL tags are applied has resulted in data that is often difficult for both human and machine readers to interpret. An approved software product list, submission-blocking powers and potential penalties for non-compliant developers are all among the enforcement tools being considered to raise standardisation levels and the quality of data.
HMRC has been working toward this since late 2024, with an initial phase covering accounts adjustments and capital allowances published in July 2025. The full rollout is planned in stages through to a live pilot period from October 2027 to September 2028.
This is a welcome step forward for structured data quality in the UK tax system. Improving the consistentcy of tagged XBRL data will improve HMRC’s ability to process and analyse returns efficiently, reduce errors, and, crucially, help close a Corporation Tax gap that stood at £18.6 billion in 2023–24.
Read more here.
