IHTM14692 | Lifetime transfers: specific lifetime reliefs: double charges relief: applying the relief
From HM Revenue & Customs · Inheritance Tax Manual
When a double charge arises:
retain the charge on the transfer which produces the higher overall amount of Inheritance Tax, and
reduce the other transfer to nil.
There is an exception in certain discretionary trust cases (IHTM14732).
Where you:
retain the later transfer within the Inheritance Tax charge, and
tax has been paid on the earlier transfer,
you may allow credit for some or all of that tax.