138Leases
(1)Where the transferred property is the interest of a lessee under a lease the duration of which at the time of the chargeable transfer does not exceed fifty years, then for the purposes of section 131 above the market value of the interest on the relevant date shall be taken to be increased by an amount equal to the appropriate fraction of the market value of the interest at the time of the chargeable transfer.
(2)In subsection (1) above, " the appropriate fraction " means the fraction—
where
P(1) is the percentage that would be derived from the Table in paragraph 1 of Schedule 3 to the [1979 c. 14.] Capital Gains Tax Act 1979 for the duration of the lease at the time of the chargeable transfer, and
P(2) is the percentage that would be so derived for the duration of the lease on the relevant date.