IHTM34152 | Sales: date of sale
From HM Revenue & Customs · Inheritance Tax Manual
The date of sale is either
the date of the contract note, or
the date on which any option to sell or purchase was granted, (IHTA/S189)
In the case of appropriations (IHTM34153) the date of sale is the date of appropriation (Re Charteris, Charteris v Biddulph [1917] 2 Ch 379). Formal evidence, such as an instrument of appropriation, will normally exist to demonstrate that steps were taken to vest assets in the legatee.