IHTM02031 | Communications: The general rule on disclosure and its operation: disclosure - the general rule and its operation
From HM Revenue & Customs · Inheritance Tax Manual
The general rule is that
you must not disclose information in HMRC Accounts (including the addresses of liable persons, their occupation or their financial circumstances) without the written authority of at least one of the
personal representatives (IHTM05012), or
other persons by whom the accounts were delivered
and if all such persons are dead