IHTM25302 | The ownership test: Meaning of ownership
From HM Revenue & Customs · Inheritance Tax Manual
For the purposes of the ownership test (IHTM25301) (including the three situations where the general rule is relaxed) we consider ownership to have the following meaning
in the case of settled property in which there is no qualifying interest in possession, legal ownership by the trustees,
In view of IHTA84/S91, where an unadministered residuary estate (IHTM22025) includes business property, a residuary beneficiary is treated as owning the business property, or an appropriate share of it.