Unscrambling a Reversionary Lease Scheme

A client entered into a Reversionary Lease arrangement in March 1999 with the lease commencing in March 2019. The reversionary lease was given to the son who is unmarried, no children and doesn’t live in the property - current value £700k.
Client paid POAT from its introduction until lease fell in and now a market value rent is accruing so as to remain outside the GWR provisions.
Following the introduction of the TNRB, RNRB and TRNRB however, no IHT would be payable if the property was back in the estate of the client but dealing with the inherent capital gains in the leasehold interest is proving tricky.
Has anyone else unscrambled such an arrangement to put the property back into the hands of the original owner?

Kurt Lee
Lester Aldridge LLP