HMRC has launched a consultation on plans to modernise and standardise the way companies prepare and submit corporation tax returns, as a further step in the UK’s move towards a fully digital, data-driven tax system.
The proposals focus on introducing a prescribed format for tax computations and requiring amendments to be submitted online, with the consultation open until 2 June 2026.
Proposed changes to company tax return rules
At present, companies submit corporation tax returns using the CT600, supported by accounts and tax computations in iXBRL format.
While tagging requirements already exist, HMRC allows a degree of flexibility in how computations are presented. According to HMRC, this has led to significant variation in practice, with similar information being reported in different ways or, in some cases, not clearly identified at all. This inconsistency makes it more difficult for HMRC to interpret data efficiently and limits its ability to use automation and analytics to assess risk and compliance.
To address this, HMRC is proposing the introduction of a standardised, fully tagged format for tax computations, referred to as “full prescription”. Under this approach, companies would be required to present their computations using a defined structure and consistent tagging, removing much of the current discretion in how information is organised. HMRC has been developing these proposals with software providers and professional bodies since 2024 and has already introduced more prescriptive requirements in specific areas, such as capital allowances and accounts adjustments, which form the basis for the wider reform.
The proposed implementation timeline reflects the scale of change. HMRC intends to work with stakeholders during 2026 to refine the technical specifications, publish final requirements by September 2026, and allow a build and testing period through to September 2027. A live pilot phase would then run from October 2027 to September 2028, during which returns would be expected to comply with the new format before any formal enforcement begins.
Alongside standardisation, HMRC is considering a stronger compliance framework. Options under consultation include introducing an approved list of corporation tax software products that meet HMRC’s specifications, blocking submissions that do not meet required standards in serious cases, and applying penalties to software providers where there are repeated or deliberate failures to comply.
HMRC has indicated that any enforcement measures would be proportionate, but the direction of travel points towards tighter control at the point of submission.
The consultation also proposes making it mandatory to file amendments to company tax returns online. Currently, amendments can be made by post or through written correspondence, which HMRC says can lead to errors, delays and uncertainty about whether a valid amendment has been made. Moving to a fully digital amendment process is intended to improve accuracy and processing times, although exemptions are proposed for cases such as ongoing enquiries and situations involving digital exclusion.
Next Steps
For businesses and advisers, the changes are likely to have practical implications for systems, processes and software. While much of the compliance burden will fall on software providers, companies will need to ensure that their internal tax reporting aligns with the new requirements and that their chosen software is compatible with HMRC’s standards.
The next step is for stakeholders to respond to the consultation before the June 2026 deadline. HMRC will then refine its proposals, with detailed technical specifications expected later in the year. Although implementation is staged over several years, the reforms represent a clear shift towards more standardised, digital corporation tax reporting in the UK.
Author
Gill Laing is a qualified Legal Researcher & Analyst with niche specialisms in Law, Tax, Human Resources, Immigration & Employment Law.
Gill is a Multiple Business Owner and the Managing Director of Prof Services Limited - a Marketing & Content Agency for the Professional Services Sector.
