IHTA84/S91 is relevant when a person ("the beneficiary") would
have been entitled to the whole or part of the residue of the
estate of a deceased person if the administration of that estate
had been completed
The effect of IHTA84/S91 is that for IHT purposes the beneficiary's interest whether limited or absolute is treated as a direct interest (and not merely a right) in the assets constituting the unadministered estate.