Practice evidence trail

CT600 submission evidence is part of the client file, not an afterthought.

Accountancy practices need a clear record of what was approved, what was filed through Government Gateway, what HMRC acknowledged, and what happened if the return was rejected or amended.

What counts as submission evidence?

Submission evidence is the practical record that the CT600 filing workflow happened properly. It includes the return package the client approved, the data sent to HMRC, the filing timestamp, the HMRC acknowledgement or rejection response, and any follow-up action.

GOV.UK says an online Company Tax Return submission receives an acknowledgement of receipt. It also makes clear that acknowledgement does not mean HMRC has agreed the figures. That distinction matters for client communication and for the practice file.

The risk of thin evidence

A practice can file a correct return and still have a poor file if it cannot later show the route from client data to submitted CT600. Thin evidence creates friction when a client asks what was filed, when HMRC raises a question, when a partner reviews quality, or when a return needs amending.

The risk is higher with Corporation Tax because the return package may contain accounts, computations, iXBRL attachments, supplementary pages, and relief claims. A single final tax number is not enough.

What to keep before submission

  • Final accounts and Corporation Tax computation reviewed for the filing period.
  • CT600 preview or export showing the figures to be filed.
  • Supplementary pages and the reasons they are included or excluded.
  • Review notes for judgement areas such as director loans, losses, R&D, capital allowances, group relief, or special regimes.
  • Client or director approval of the return package.
  • Authority to file through the practice or agent route.

What to keep after submission

  • Submission date and time.
  • HMRC acknowledgement of receipt, or the rejection response if the filing failed.
  • The submitted CT600, computation, accounts, and supplementary pages.
  • Any payment, repayment, or interest implications discussed with the client.
  • Follow-up tasks, including rejected-return fixes or amendment notes.

How to handle a rejection response

A rejection response should stay attached to the job. Do not overwrite the file with only the final successful state. Keep the first response, diagnose the issue, record the fix, and keep the later acknowledgement.

In practice, rejected CT600s often involve one of five areas: data validation, period mismatch, attachment format, credentials or agent authority, or temporary service issues. The evidence trail should show which one applied and what changed before re-submission.

Client-facing wording

Practices should avoid implying that HMRC has approved the tax position just because a return was received. A clearer client message is:

"Your Company Tax Return has been submitted and HMRC has acknowledged receipt. This acknowledgement confirms receipt of the return; it is not confirmation that HMRC has agreed the figures. We will keep the submission evidence with your Corporation Tax file."

What good CT600 software should provide

Practice software should make evidence collection a natural part of the workflow, especially where a team prepares returns across many clients.

  • A reviewable return package before filing.
  • Clear status for draft, approved, submitted, rejected, amended, and accepted-for-receipt states.
  • Preserved submission and rejection responses.
  • Links between CT600 boxes, computations, attachments, and supplementary pages.
  • Team-visible audit trail for preparer, reviewer, client approval, and submission.

How Robocount helps practices

Robocount is built for Corporation Tax filing workflows that need review, submission, and evidence in one place. It is not just a form entry screen. It helps teams keep the CT600 package, iXBRL attachments, supplementary pages, validation, approval, and Government Gateway submission evidence together.

  • Supports repeatable CT600 preparation and review.
  • Keeps supplementary-page decisions close to the main return.
  • Gives practices a clearer trail for approval and filing evidence.
  • Supports API and MCP-native filing workflows where AI or automation prepares work for human review.

FAQ

Does an HMRC acknowledgement prove the CT600 is correct?

No. GOV.UK says the acknowledgement confirms receipt and does not mean HMRC has agreed the figures. HMRC may still amend obvious errors, correct items it believes are incorrect, or enquire into the return.

Should a practice keep rejected submission responses?

Yes. The rejection response explains what happened before the successful filing. Keep it with the diagnosis, fix, re-submission evidence, and any deadline-risk communication.

What evidence should the client receive?

The client normally needs a concise confirmation that the return has been submitted, the HMRC acknowledgement has been received, and any payment or repayment action is clear. The full working evidence should remain on the practice file.

Why does this matter for AI-assisted CT600 workflows?

AI-assisted filing needs an especially clear evidence trail. The practice still needs to know what was prepared, what was reviewed by a human, what was approved by the client, and what was actually submitted.

Useful official references

This guide is general product and filing workflow information, not tax advice. Check current HMRC guidance and the facts of the company before filing.