3" Attachable earnings", in relation to a pay-day, are the earnings which remain payable to the debtor on that day after deduction by the employer of—
(a)income tax;
(b)contributions under any of the following enactments—
the National Insurance Act 1965,
the National Insurance (Industrial Injuries) Act 1965, or
the National Health Service Contributions Act 1965 ;
(c)amounts deductible under any enactment, or in pursuance of a request in writing by the debtor, for the purposes of a superannuation scheme within the meaning of the [1959 c. 69.] Wages Councils Act 1959.