IHTM30375 | Special rules: settled property - sales and mortgages of reversionary interests
From HM Revenue & Customs · Inheritance Tax Manual
There is a further relief, which is included only for completeness as you are unlikely to see it in practice. It relates to the tax charge:
There is a tax relief (IHTM16232) in these circumstances.
The relief is applied in the same way as that afforded by IHTA84/S40(2)(d) FA 1969 for Estate Duty. Any sum repayable under this practice would not carry interest.