For the purposes of the advance payments code interest on any sum held by a street works authority shall be calculated in respect of each financial year during which it accrues at the appropriate rate prevailing at the commencement of that financial year.
In this section "the appropriate rate" means the rate at the material time determined by the Treasury in respect of local loans for periods of 10 years on the security of local rates (being a determination under section 6(2) of the National Loans Act 1968, and subject to any relevant direction under the said section 6(2)).