London, June 22: Keir Starmer on Monday announced his resignation as British Prime Minister and the Leader of the Labour Party, setting out a timetable for his successor to be elected in the coming weeks and be in place by September.   The 63-year-old said he will remain in post until a new leader and PM is elected by the governing party and pledged his "full and unequivocal support" to the new leader to "ensure an orderly handover of power". Andy Burnham, who returns to the House of Commons after winning a crucial by-election last week, is seen as the frontrunner in the race to replace him at 10 Downing Street.