IHTM27053 | Foreign property: valuation of assets: foreign rulers and sovereign immunity
From HM Revenue & Customs · Inheritance Tax Manual
Any case that involves:
a transfer (either during their lifetime or on their death) of assets held in the UK by a foreign ruler,
the question of how assets held in the UK by a foreign ruler are treated for Inheritance Tax purposes,
a claim that although UK assets were held in the name of a foreign ruler they were not in their beneficial ownership, or
in any other circumstances, the question of sovereign immunity for tax purposes
must be referred immediately to Technical.