23. Every document purporting to be an instrument issued by the Authority or the Executive and to be sealed with the seal of the Authority or the Executive and authenticated in accordance with the provisions of paragraph 11 of Schedule 3 or of Article 17(1) or to be signed on behalf of the Authority or the Executive by their Secretary or by some other person authorised by the Authority or the Executive, either generally or specially, to act for that purpose shall be received in evidence and be deemed to be such a document without further proof unless the contrary is proved.