(1) In this section 'market value', in relation to a building, structure or house, means the price which the unencumbered fee simple of the building, structure or house would fetch if sold in the open market in such manner and subject to such conditions as might reasonably be calculated to obtain for the vendor the best price for the building, structure or house, less the part of that price which would be attributable to the acquisition of, or of rights in or over, the land on which the building, structure or house is constructed.

(2) Subject to subsection (4), a lease of a house is a qualifying lease for the purposes of this Chapter where the consideration for the grant of the lease consists -

(a) solely of periodic payments all of which are or are to be treated as rent for the purposes of Chapter 8 of Part 4, or

(b) of payments of the kind mentioned in paragraph (a), together with a payment by means of a premium which -

(i) in the case of the construction of a house, does not exceed 10 per cent of the relevant cost of the house,

(ii) in the case of the conversion of a building into a house, does not exceed 10 per cent of the market value of the house at the time the conversion is completed, and