STSM021150 | Scope of stamp duty on shares: stamp duty: basics of a charge: grant of an option
From HM Revenue & Customs · Stamp Taxes on Shares Manual
A document under which an option is granted or released is chargeable with Stamp Duty on the amount paid for the grant or release. (George Wimpey & Co Ltd v IRC [1975] 2 All ER 45).
But following FA03/S125 Stamp Duty now only applies to an instrument granting or releasing an option in or over stock or marketable securities.