As soon as practicable in each financial year each local authority that is entitled to a subsidy under paragraph (c) of subsection one of this section shall supply to the Board a certificate by the Chairman or Treasurer of the local authority showing the general rates (excluding money levied for hospital purposes or for the purposes of any other local authority) and separate and special rates for roading purposes that were levied by the local authority for any preceding financial year and were actually collected by the local authority, or by another local authority as its agent under section thirty of the Finance Act 1941, during the financial year immediately preceding that in which the subsidy is due, and the Board shall calculate the subsidy payable to the local authority on the basis of that certificate.”