4SA person may be appointed as a member of the Authority under paragraph 2 above only if he is a member of the council or one of the councils by whom he is so appointed; and no person who is for the time being a member, officer or employee of the Strathclyde Passenger Transport Executive or who is for the time being an employee of a subsidiary of that Executive shall be appointed as a member of the Authority, and any person appointed to be a member of the Authority who subsequently becomes a member, officer or employee of that Executive or such a subsidiary shall forthwith vacate his membership of the Authority.