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HMRC internal manual

Inheritance Tax Manual

Reconsideration by HMRC: effect of a sale

Where there has been an agreement (IHTM30442) you should not reopen the question of value to claim additional tax because of a sale entered into after the date of the agreement or assessment, even though negotiations for the sale short of a binding contract may have been in hand prior to that date. In fixing the critical date by reference to the contract it is implicit that the contract is duly implemented; otherwise, of course, there is no sale.

Where the contract was entered into before the date of the agreement or assessment but we were not informed until later, you should not regard the agreement or assessment as a bar to the value being reopened if the sale price is substantially higher than the value accepted.