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HMRC internal manual

Inheritance Tax Manual

Communications: Incoming telephone calls: requests for information where the caller cannot be verified

In any case where the parties want to know any information we hold on the file you must return their call before you give it (IHTM02045).

If the information given by the caller does not match that on the file you should treat the identity of the caller as not verified (IHTM02047). You must follow the procedures at IHTM02047.