28The main subject-matter of a transaction is also taken to consist of or include an interest in a dwelling if—
(a)substantial performance of a contract constitutes the effective date of that transaction by virtue of a relevant deeming provision,
(b)the main subject-matter of the transaction consists of or includes an interest in a building, or a part of a building, that is to be constructed or adapted under the contract for use as a single dwelling, and
(c)construction or adaptation of the building, or the part of a building, has not begun by the time the contract is substantially performed.