IHTM11075 | Annuity to spouse or civil partner: annuity secured by personal covenant
From HM Revenue & Customs · Inheritance Tax Manual
If the annuity (IHTM16211) is secured merely by personal covenant and is not a charge on any property, the gift to the annuitant should be treated as a legacy equivalent to the open market value of the annuity. The Actuarial Group is responsible for the valuation.
You should first ask the taxpayer or their agents to
state the date of birth of the annuitant (IHTM16211)
state the gender of the annuitant (if unknown), and
provide a reasoned estimate of the open market value of the annuity
When that information is received, you should refer to the case to the Actuarial Group.