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HMRC internal manual

Company Taxation Manual

Corporation Tax self-assessment (CTSA): Assessments: General

The self assessment contained in a company tax return creates a legal charge to tax.  Subject to the right to make a discovery assessment (see CTM95030 onwards) or discovery determination (see CTM95500 onwards) the return is final once made, unless within the relevant time limits:

  • the company amends it (see CTM93300 and COM23010)
  • an officer decides to enquire into it
  • the conclusions stated at the end of an enquiry into a return for a different period require a consequential amendment to it (FA98/SCH18/PARA34 (2A).

See the Enquiry Manual for guidance on opening and conducting enquiries.