(1) In this section -
"conversion expenditure" means, subject to subsection (2), expenditure incurred on -
(a) the conversion into a house of a building or part of a building -
(i) the site of which is wholly within a qualifying area, or which fronts on to a qualifying street, and
(ii) which has not been previously in use as a dwelling,
and
(b) the conversion into 2 or more houses of a building or part of a building -
(i) the site of which is wholly within a qualifying area, or which fronts on to a qualifying street, and
(ii) which before the conversion had not been in use as a dwelling or had been in use as a single dwelling,
and references in this section and in section 372J to "conversion", "conversion into a house" and "expenditure incurred on conversion" shall be construed accordingly;
"qualifying lease", in relation to a house, means, subject to section 372J(2), a lease of the house the consideration for the grant of which consists -
(a) solely of periodic payments all of wh