For each sitting of a value added tax tribunal the chairman shall be either the President or, if so authorised by the President, a member of the appropriate panel of chairmen constituted in accordance with paragraph 7 of this Schedule; and any other member of the tribunal shall be a person selected from the appropriate panel of other members so constituted, the selection being made either by the President or by a member of the panel of chairmen, authorised by the President to make it.