IHTM21047 | Household goods and personal goods: valuation and technical issues: situs of works of art owned overseas
From HM Revenue & Customs · Inheritance Tax Manual
For Inheritance Tax purposes, household and personal goods are situated where they happen to be at the relevant date. The exception to this is that, under IHTA84/S5(1)(b), 64(2) and 272 tax is not charged in connection with a death or a ten-year anniversary on a work of art if the following three conditions apply:
It is normally kept outside the UK
It would become liable to Inheritance Tax solely because it happened to be in the UK at the relevant date, and
It was brought here for public exhibition, cleaning or restoration (and no other purpose).
If you receive any case where this exemption is mentioned or might apply you must refer it to Heritage immediately.