“(1) An averment in any process in proceedings under the customs and excise Acts—..... (d) that the Commissioners have or have not been satisfied as to any matter as to which they are required by any provision of those Acts to be satisfied; or... shall, until the contrary is proved, be sufficient evidence of the matter in question. (2) Where in any proceedings relating to customs or excise any question arises as to the place from which any goods have been brought or as to whether or not— (a) any duty has been paid or secured in respect of any goods; or ... then, where those proceedings are brought by or against the Commissioners, a law officer of the Crown or an officer, or against any other person in respect of anything purporting to have been done in pursuance of any power or duty conferred or imposed on him by or under the customs and excise Acts, the burden of proof shall lie upon the other party to the proceedings”