IHTM27273 | Foreign property: specific property of visiting forces and staff of Allied Headquarters: assets excluded from UK Inheritance Tax
From HM Revenue & Customs · Inheritance Tax Manual
IHTA84/S155 (1) says that assets of qualifying persons (IHTM27274), that are eligible for this exclusion from the tax, are:
emoluments paid by the government of any designated country to a member of a visiting force of the country
tangible movable property (for example furniture, cars) which is in the UK solely because of the member’s duty here.