Not less than six months before the date on which an archbishop is required to vacate his office in accordance with section 1 of the M1 Ecclesiastical Offices (Age Limit) Measure 1975, the archbishop shall tender his resignation to Her Majesty in a written instrument in the prescribed form and Her Majesty may by Order in Council declare the archbishopric vacant as from that date or, if Her Majesty decides to exercise Her discretion under section 2 thereof, as from such later date as Her Majesty may determine under that section.