Sums to be invested under section 17 of this Act shall be invested—
(a)in Parliamentary securities created or issued under the authority of an Act of Parliament where those securities are securities for the interest on which provision is made by Parliament or are securities directly chargeable on the Consolidated Fund or on the National Loans Fund with recourse to the Consolidated Fund, or
(b)in stock or debentures or other securities expressly guaranteed by authority of Parliament or the due payment of the interest on which is expressly guaranteed by authority of Parliament, or
(c)in securities which are issued in respect of a loan raised by the Government of Northern Ireland or the interest on which is for the time being guaranteed by the Parliament of Northern Ireland.