SDLTM00290 | Scope: What is chargeable: Land transactions: Main subject matter FA03/S43(6)
From HM Revenue & Customs · Stamp Duty Land Tax Manual
Main subject matter means the chargeable interest acquired in a land transaction. Any interest or right appurtenant or pertaining to it that is acquired with it, but not part of the main subject matter of the transaction, is not taken into account when considering whether the land acquired is residential or non-residential/mixed.