158.—(1) The consideration for the offer by a qualifying person (or his successor in title or a person deriving title under him or his successor) referred to in section 157(4)(a), to reconvey or surrender his interest to the landlord shall be such amount as may be agreed between the parties or determined by the district valuer as being the amount which is to be taken as the value of the qualifying dwelling-house at the time the offer is made.
(2) That value shall be taken to be the price which, at that time, the interest to be reconveyed or surrendered would realise if sold on the open market by a willing vendor, on the assumption that any liability under—
(a)a covenant imposed by virtue of section 155 (repayment of discount on early disposal),
would be discharged by the vendor.
(3) If the landlord accepts the offer, no payment shall be required in pursuance of any such covenant as is mentioned in subsection (2), but the consideration shall be reduced, subject to subsection (4), by such amount (if any) as, on a disposal made at the time the offer was made, being a relevant disposal which is not an exempted disposal, would fall to be paid under that covenant.
(4) Where there is a charge on the qualifying dwelling-house having priority over the charge to secure payment of the sum due under the covenant mentioned in subsection (2), the consideration shall not be reduced under subsection (3) below the amount necessary to discharge the outstanding sum secured by the first-mentioned charge at the date of the offer to reconvey or surrender.