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HMRC internal manual

Company Taxation Manual

HM Revenue & Customs
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Corporation Tax self-assessment (CTSA): Assessments: Discovery - general


Under CTSA most assessments are SA.

However, you can make “discovery” assessments in certain circumstances. For accounting periods within CTSA the rules contained in Paragraph 41 replace the “discovery” provisions in “old” TMA70/S29. (Note: “new” TMA70/S29 does not apply to companies.)

Subject to restrictions in FA98/SCH18/PARA43 - 45 you can make a “discovery assessment” under Paragraph 41 (1) to make good to the Crown a loss of tax on discovering that:

  1. an amount which ought to have been assessed to tax has not been assessed,
  2. an assessment to tax is, or has become insufficient,
  3. relief given is, or has become excessive.

A discovery assessment is only appropriate when a “discovery” leads to additional tax liability on the company for that accounting period.