IHTM30372 | Special rules: voidable transfers
From HM Revenue & Customs · Inheritance Tax Manual
Where a voidable chargeable transfer (IHTM14890) is subsequently set aside by virtue of any enactment or rule of law, any tax paid on it is repayable.
Tax repayable under IHTA84/S150 carries interest (free of income tax) from the date on which the claim for repayment is made.