Loss on sale of land: changes in the interest or underlying land: leases
You must make an addition to the sale price (IHTM33072) where the interest is a leasehold with not more than fifty years to run at the date of death, IHTA84/S194 (1).
The amount of addition is the ‘appropriate fraction’ of the value on death (IHTM33100) of the interest in land. The appropriate fraction is:
(P1 - P2) ÷ P1