Beta This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Company Taxation Manual

Corporation Tax self-assessment (CTSA): Assessments: Agreed figures - CT Pay and File (CTPF) periods

For CTPF accounting periods you should make assessments on agreed figures without delay, even though the company may already have paid the full tax liability.

You should make a formal assessment when there is no liability to CT unless the company has no profits of any description.