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HMRC internal manual

Inheritance Tax Manual

Other issues: disclosure of TNRB calculations to other liable persons

The claim to transfer unused nil rate band is made by the personal representatives  (or other liable persons) and you should treat this in the same way as any other information provided by a taxpayer. Just as with aggregable property where we need to tell all those liable for tax on a case what the total value for each component of the estate is, so that they can see how their individual liability is calculated; so we have to tell all those liable for tax what the revised nil rate band is. This will allow them to work out what the transferable amount is; but not how that amount has been arrived at.