Where, in accordance with section 302, 319 or 325, a decision or determination is varied or reversed by a deciding officer, an appeals officer or a designated person (as the case may be) so as to disallow or reduce any benefit, assistance, child benefit, working family payment, continued payment for qualified children or back to work family dividend paid or payable to a person -

(a) any benefit paid in pursuance of the original decision shall be repayable to the Social Insurance Fund to the extent to which it would not have been payable if the decision on the appeal or revision had been given in the first instance and the person and any other person to whom the benefit was paid on behalf of that person, or the personal representative of that person, shall be liable to pay to the Fund, on demand made in that behalf by an officer of the Minister, the sum so repayable,