IHTM40014 | Clearance certificates: what is not covered by a clearance certificate?
From HM Revenue & Customs · Inheritance Tax Manual
The clearance certificate means that the taxpayer will not have to pay any further tax on the transfer described in the certificate, unless IHTA84/S239 (4) applies, where
there has been fraud or failure to disclose material facts (IHTM40143)
additional assets (IHTM40142) are later shown to have been included in the transfer
too great an increase in the nil rate band has been claimed on the death of the surviving spouse (IHTM43067)
further tax becomes payable as a result of statutory amendments after issue (IHTM40147)