Related property: when to use the special rule?
You should use the special rule when the items of property (IHTM04030) that are being aggregated for valuation purposes under the related property rules are identical in their attributes. It will mainly apply to shares of the same class. But it will also apply to stock, debentures, and undivided shares of property.
The issue of whether IHTA84/S161(4) applies to shares of land was considered by the Special Commissioners in Arkwright and another v Inland Revenue Commissioners  UKSPC00392,  STC (SCD) 89. There it was held that whilst IHTA1984/S161(4) could apply to property which had a distinct individual existence as a unit, such as unit trusts or a set of furniture (for example twelve dining chairs), it did not apply to fractions of units.
Although this issue was not considered further when the Revenue’s appeal against the decision was heard by the High Court, there is still some question whether IHTA1984/S161(4) can apply to shares of land. For this reason, any cases that involve the application of IHTA1984/S161(4) should be referred to Litigation.