For this part, an amount is a
"retention amount" for a building contract if—
(a) the amount is payable as part of the contract price under the building contract, but, under the contract, may be withheld from payment to the contracted party for the building contract—(i) during the progress of the building work the subject of the contract; or(ii) for a period (a
"maintenance period" ) after the completion of the building work; or(iii) both during the progress of the building work and for a maintenance period; and
(b) the purpose of withholding the amount is to give financial protection to the contracting party in relation to the need to correct defects in the building work, or otherwise to secure, wholly or partly, the performance of the contract.