From HM Revenue & Customs · Inheritance Tax Manual
You should refer any cases to Technical
which do not satisfy the requirements (IHTM11124), or
about which you are doubtful
You should also refer
gifts to charities by an instrument of variation (IHTM35011) or an appointment by executors/ trustees where property is held on trusts (IHTM11161) for charitable purposes but which include objects outside the UK.
any case in which a charity beneficiary settles a claim (IHTM11026) against the deceased’s estate.