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Consultation response: modernising and standardising company tax returns

1 June, 2026

The ATT has responded to HMRC's consultation on Modernising and standardising company tax returns, published following the Government’s announcement at Budget 2025 that Corporation Tax computations will move to a prescribed format. 

The consultation seeks views on the proposed implementation timelines for the prescription of Corporation Tax computations, the arrangements that HMRC will introduce to ensure a smooth transition from the current rules, and HMRC's proposals for proportionate enforcement mechanisms to support compliance. It also considers mandatory online filing for amended company tax returns and invites feedback on potential issues.

The proposals would require all companies to submit computations in a standardised fully tagged format. This is intended to reduce errors, improve clarity for taxpayers and agents, and allow HMRC to process returns more efficiently. 

The key themes from the ATT’s response include:

  • We support the overall objective of standardising Corporation Tax computations and recognise the potential benefits in terms of improved accuracy, consistency, and efficiency. 
  • We have concerns that the proposed 6-month collaborative development period may not be sufficient, given the complexity and different computational areas involved. We recommend that the timeline is kept under review and remains flexible to ensure that all issues identified during the development period are properly resolved before progressing.
  • While stakeholder roundtables can be effective, their success will depend on appropriate representation and sufficient preparation time. The current approach risks limiting meaningful engagement, particularly for those in practice with competing time pressures.
  • The proposed implementation timelines more broadly should remain flexible and take account of wider ongoing reforms and demands on software providers, agents and taxpayers.
  • We welcome the introduction of a live pilot phase but consider that a longer pilot period may be necessary to allow taxpayers, agents and software providers to adapt systems and processes. Attempting to implement changes retrospectively for accounting periods already underway could create significant practical challenges.
  • We recognise the potential value of an Approved Corporation Tax Software Product List but highlight the need for clear criteria, transparency, and effective communication. Early availability of compliant software will be critical to avoid disruption and increased compliance burdens.
  • We have concerns about enforcement measures that could block submissions or require taxpayers to change software providers at short notice. Such measures could be highly disruptive and costly, and neither taxpayers nor their agents should be penalised for issues outside their control. Clear guidance and support will be essential.
  • We support the principle of locking tags within software to promote consistency, but only where the tagging framework is robust and complete. Strong testing, monitoring, and clear escalation processes will be needed to address errors.
  • We broadly support mandatory online filing of amended returns, but flexibility will be needed in cases where taxpayers face software limitations or transitional challenges. Additional support will be particularly important for unrepresented taxpayers.

Overall, while we support the direction of travel, successful implementation will depend on flexibility, clear communication, and close engagement with stakeholders to ensure the changes do not introduce unnecessary complexity or burdens.