Where an arrangement has, either before or after the commencement of this Act, been made by Her Majesty with the government of any other country or by the Postmaster-General with any other postal administration with respect to the conveyance by post of any postal packets between the British postal area and places outside that area, or between places outside that area, whether through that area or not, the Treasury may by warrant make such regulations as may seem to them necessary for carrying the arrangement into effect, and may make provision as to the charges for the transit of postal packets, single or in bulk, the scale of weights to be adopted, and the accounting for and paying over to any other postal administration of any money received by the Postmaster-General.