This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Inheritance Tax Manual

Estate Duty surviving spouse exemption: summary

This exemption is a carry-over from the Estate Duty regime. With certain conditions, it means that a surviving spouse’s limited interest in possession (IHTM16060) in settled property is not subject to Inheritance Tax. Although it rarely applies now you still need to be aware of the provisions. The exemption may apply on the death of the surviving spouse (IHTM04343) or when the interest of the surviving spouse terminates (IHTM04344) during their lifetime.

If you think that theexemption may be due, but the taxpayer has not deducted it, see IHTM04346.