5.—(1) The deductions to be taken from gross earnings to calculate net income for the purposes of this Part are any amount deducted from those earnings by way of—
(a)income tax;
(b)primary Class 1 contributions under the Contributions and Benefits Act or under the Great Britain Contributions and Benefits Act; or
(c)any sums paid by the non-resident parent towards an occupational pension scheme or personal pension scheme or, where that scheme is intended partly to provide a capital sum to discharge a mortgage secured upon that parent’s home, 75 per centum of any such sums.
(2) For the purposes of sub-paragraph (1)(a) amounts deducted by way of income tax shall be the amounts actually deducted, including in respect of payments which are not included as earnings in paragraph 4.
(3) Where a person is an employed earner in the Republic of Ireland the amounts deducted for income tax and primary Class 1 contributions shall be such amounts as, in the opinion of the Department, would have been deducted had the person been employed in Northern Ireland.