The Sunday Telegraph has a copy of the letter being circulated around Labour backbenchers. It says every Labour member wants the handover to be conducted in a"dignified, orderly and efficient manner''. But it says a prerequisite for that is "a clear timetable and transparent procedures''. The letter goes on: "We thereforeask the NEC, in consultation with the Prime Minister, to lay out, no later than the end of the current Parliamentary session, a clear timetable and procedure for the election of a new Labour party leader.''
Note that last bit - it leaves open the possibility for a new Labour Party leader to be a different person than the PM. So Gordon could be elected Labour leader while Tony stays as PM.