(1) Stamp duty shall not be chargeable on any instrument of transfer whereby any securities upon the sale thereof are transferred to a member firm acting on its own behalf in the ordinary course of that member firm's business or to a nominee of such member firm:
Provided that:
(a) if and to the extent that the member firm does not transfer those securities to a bona fide purchaser before the expiration of the period of one month from the date of transfer, hereinafter in this section referred to as 'the specified period', the member firm shall pay to the Commissioners within 14 days after the expiration of the specified period the amount of ad valorem duty which would have been chargeable on the transfer if this section had not been enacted;
(b) the member firm may, in relation to any such sale with a completion date not later than 30 days from the date of the contract for sale and prior to the date of the contract, elect to have such completion date treated as the date of the seco