At the end of section 12 of the Principal Act insert —
"(2) Interest is payable on the unpaid amount of a progress payment that has become due and payable in accordance with sub-section (1) at the greater of the following rates—
(a) the rate for the time being fixed under section 2 of the Penalty Interest Rates Act 1983 ; or
(b) the rate specified under the construction contract.".