4(1)The marriage value is the amount referred to in sub-paragraph (2), and the landlord’s share of the marriage value is—
(a)such proportion of that amount as is determined by agreement between the landlord and the tenant or, in default of agreement, as is determined by a leasehold valuation tribunal to be the proportion which in its opinion would have been determined by an agreement made at the valuation date between the parties on a sale on the open market by a willing seller, or
(b)50 per cent. of that amount,
whichever is the greater.
(2)The marriage value is the difference between the following amounts, namely—
(a)the aggregate of—
(i)the value of the interest of the tenant under his existing lease,
(ii)the value of the landlord’s interest in the tenant’s flat prior to the grant of the new lease, and
(iii)the values prior to the grant of that lease of all intermediate leasehold interests (if any); and
(b)the aggregate of—
(i)the value of the interest to be held by the tenant under the new lease,
(ii)the value of the landlord’s interest in the tenant’s flat once the new lease is granted, and
(iii)the values of all intermediate leasehold interests (if any) once that lease is granted.
(3)For the purposes of sub-paragraph (2)—
(a)the value of any interest of the tenant shall be determined as at the valuation date;
(b)the value of any such interest of the landlord as is mentioned in paragraph (a) or paragraph (b) of that sub-paragraph is the amount determined for the purposes of paragraph 3(1)(a) or paragraph 3(1)(b) (as the case may be); and
(c)the value of any intermediate leasehold interest shall be determined in accordance with paragraph 8, and shall be so determined as at the valuation date.