(1) In this section -

'chargeable period' means an accounting period of a company or a year of assessment;

'relevant cost', in relation to a house, means, subject to subsection (6), an amount equal to the aggregate of -

(a)

(i) where the eligible expenditure is on the construction of the house, the expenditure incurred on the acquisition of, or of rights in or over, any land on which the house is situated, or

(ii) where the eligible expenditure is conversion expenditure or refurbishment expenditure, the expenditure incurred on the acquisition of, or of rights in or over -

(I) any land on which the house is situated, and

(II) any building in which the house is comprised,

and

(b) the expenditure actually incurred on the construction of, conversion into, or, as the case may be, refurbishment of the house;

'relevant period', in relation to the incurring of eligible expenditure on or in relation to a qualifying premises or a special qualifying premises, means -