What changed on 31 March 2026
Companies House and HMRC closed the joint online service that allowed some companies to file accounts and the Company Tax Return together. GOV.UK says the service closed on 31 March 2026 and that, from 1 April 2026, companies should use commercial software to file annual accounts and Company Tax Returns with HMRC.
That change matters most for directors and small companies that previously used the free joint service. CT600 filing is now a software workflow: accounts, computations, iXBRL, the CT600, any supplementary pages, attachments, review, and Government Gateway submission.
Who is affected
The change affects companies that used the joint filing service for accounts and the Company Tax Return. If a company receives a notice to deliver a Company Tax Return, it still needs to submit the CT600 package by the deadline. The difference is the route used to prepare and file it.
Typical affected users include:
- company directors who previously self-filed using the joint online service;
- small limited companies with straightforward accounts but no tax software yet;
- bookkeepers helping clients gather accounts and Corporation Tax data;
- accountancy practices onboarding directors who can no longer use the old route;
- AI and automation workflows that need a compliant CT600 filing path.
Can you still file a paper CT600?
GOV.UK says paper filing is only available in limited situations, such as when a company cannot file online because it has a reasonable excuse or wants to file in Welsh. For normal CT600 filing, the practical answer is commercial software.
That means directors should not leave the software choice until the filing deadline. Even a simple company return can require setup, accounts data, iXBRL tagging, computations, and review before submission.
What commercial CT600 software needs to handle
The Company Tax Return is more than the main CT600 form. HMRC's own guidance describes the return package as the return form, supplementary pages, accounts, computations, and relevant information. Good software should make that whole package reviewable.
- Main CT600 preparation for the accounting period.
- Corporation Tax computation and relief calculations.
- iXBRL accounts and computation attachments where required.
- Supported CT600 supplementary pages such as CT600A, CT600C, CT600L, and others.
- Validation checks before submission.
- Government Gateway submission and response handling.
- An audit trail that explains what was filed and why.
Directors: what to prepare before choosing software
If you are moving from the old joint filing service, start with the filing data rather than the software form. The return will be easier if you gather the accounting period, Companies House accounts position, profit and loss figures, balance sheet, Corporation Tax adjustments, director loan details, and any reliefs or special cases.
Pay particular attention to anything that creates a supplementary page. Owner-managed companies often need extra review for overdrawn directors' loan accounts, group relief, R&D claims, creative industry relief, or residential property developer tax. Those are not areas to treat as casual add-ons.
Practices: why this creates onboarding demand
The closure of the joint service is likely to push more directors toward accountants and software-led support. Some will have straightforward returns. Others will arrive close to deadline with missing computations, accounts questions, or supplementary-page issues.
For practices, the commercial opportunity is not just filing volume. It is repeatable CT600 intake: collect the right data, review the risk areas, prepare the return package, file through HMRC, and keep evidence for the next year.
How Robocount fits the new filing route
Robocount is built for the post-joint-service CT600 workflow. It focuses on UK Corporation Tax returns, not a generic accounting suite bolted onto a tax form.
- Prepare and review CT600 returns in a browser-based workflow.
- Connect computations, iXBRL attachments, and supplementary pages.
- Support accountancy practice and company director filing routes.
- Expose API and MCP-native surfaces for AI-assisted CT600 workflows.
- Keep review evidence visible before Government Gateway submission.
FAQ
Did HMRC close the free Company Tax Return filing service?
GOV.UK says the service to file accounts and the Company Tax Return together closed on 31 March 2026. From 1 April 2026, companies should use commercial software for annual accounts and Company Tax Returns with HMRC.
Can I still file accounts and CT600 together?
The old joint service has closed. You still need to file accounts with Companies House and the Company Tax Return with HMRC, but the route depends on the software and the filing requirements for the company.
What if I need to amend or re-file a rejected return?
HMRC has published specific guidance for companies that previously used the closed service, including amendments and rejected returns. Check that guidance before choosing the filing route.
Is Robocount only for accountants?
No. Robocount is designed for both accountancy practices and company directors, with workflows for CT600 preparation, review, and filing. Practices get repeatable client workflows; directors get a clearer route through Corporation Tax filing.
Useful official references
- GOV.UK: closure of the service to file your company accounts and tax return
- GOV.UK: File your accounts and Company Tax Return
- HMRC: filing your Company Tax Return online
- HMRC Company Tax Return guide
This guide is general product and filing workflow information, not tax advice. Check the current GOV.UK guidance and the facts of the company before filing.