The official mark of any sum on any postal packet as due in respect of that packet, whether the mark is the mark of the Post Office or of any other postal administration and whether the sum is marked as being due to the Postmaster-General or otherwise, shall in every court in the British postal area be sufficient proof of the liability of the packet to the sum so marked unless the contrary is shown, . . . F2

In any proceedings for the recovery of postage or other sums due in respect of postal packets, the production of the packet in respect of which any such postage or sum is sought to be recovered having thereon a stamp or other endorsement of the Post Office or any other postal administration indicating that the packet has been refused or rejected or is unclaimed or cannot for any other reason be delivered, shall be sufficient proof of the fact indicated unless the contrary is shown.

In any such proceedings as aforesaid, F3a certificate of the Post Office that any mark, stamp or endorsement is such a mark, stamp or endorsement as is mentioned in the foregoing provisions of this section shall be sufficient proof thereof unless the contrary is shown.

In any such proceedings as aforesaid, the person from whom any postal packet in respect of which any postage or sum is sought to be recovered purports to have come shall, until the contrary is proved, be deemed to be the sender of the packet.