(1) The Collecting Officer to whom a person makes payments in compliance with an attachment of earnings order shall after deducting such court fees, if any in respect of proceedings for or arising out of the order, as are deductible from those payments, pay the remaining sums to the persons entitled.
(2) Any sum paid to the Collecting Officer under an attachment of earnings order made to secure maintenance payments shall, when paid to the person entitled to receive those payments, be deemed to be payments made by the debtor so as to discharge—
(a) first, any sums due and unpaid under the maintenance order, a sum due at an earlier date being discharged before a sum due at a later date; and
(b) secondly, any costs incurred in proceedings related to the maintenance order which were payable by the debtor when the attachment of earnings order was made or last varied.