The Road Works (Sharing of Costs of Works) (Scotland) Regulations 1992

9.  Allowable costs under any of the provisions of these Regulations shall be payable as follows:—

(a) in the case of any payments due from an authority pursuant to regulations 3 and 6, the authority may pay to the undertaker a sum equal to 75 per cent of the estimate of 82 per cent of the allowable costs in a single lump sum before the works begin or, if the authority and undertaker so agree in the case of works of an estimated duration of more than three months, by instalments of such amounts payable at such times during the execution of the works as the authority and undertaker agree;

(b) after the works have been completed, the person to whom the allowable costs are due (“the creditor”) shall issue to the person from whom they are due (“the debtor”) an account of the allowable costs and within 35 days of that account having been issued the debtor shall pay to the creditor a sum equal to the allowable costs, provided that in any case where an authority has made a payment or payments pursuant to sub-paragraph (a) above—

(i) the authority shall pay to the undertaker the balance of the estimate together with any further sum equal to the amount by which the proportion of allowable costs to which the undertaker is entitled exceeds the estimate;

(ii) the undertaker shall refund to the authority a sum equal to the amount by which the sum paid by the authority pursuant to sub-paragraph (a) of this regulation exceeds the proportion of allowable costs to which he is entitled.