RM3724 | Reviewing the claim form: When to inform the donor's GCD
From HM Revenue & Customs · Repayment Claims Manual
If a minor is given £ 20,000 or more
send details to the GCD of the person(s) who gave the money or assets (the donor)
ask the donor’s GCD, if they have any doubt that the donor had enough money to make the gift,
to tell you
to send you their papers on loan
when you receive the donor’s papers send them with your papers to HMRC Trusts Head Office Edinburgh.
If the gift is £ 50,000 or more tell the GCD to follow the advice at AP4068.