SolvedCH63140 | Penalties for Failure to File on Time: Calculating the penalty: Penalty reductions for disclosure: Unprompted and prompted disclosure
From HM Revenue & Customs · Compliance Handbook
A disclosure is unprompted if, when the person made it, they had no reason to believe that we had discovered or were about to discover the information that they withheld by failing to make the return.
Otherwise it is a prompted disclosure. We want to encourage unprompted disclosures.
You need to consider all the facts before deciding whether a disclosure is unprompted or prompted. You should apply a common sense approach in deciding whether or not a disclosure is unprompted and avoid making hasty judgements.
For guidance on how to decide whether a disclosure is unprompted or prompted, see CH63160.