—(1)  A member who is entitled to withdraw the sum standing to his credit in the Fund under section 15(2)(a), (3) or (4) may, in addition to the minimum sum that the member is required to set aside under section 15, set aside in accordance with regulations made under this Act, the balance or any part of the balance of the sum which the member is entitled to withdraw under section 15(2)(a), (3) or (4) (referred to in this section as the additional sum).