The result of the Labour Party leadership contest will not be determined for another four months, it was announced yesterday.

The party's ruling national executive committee (NEC) set a timetable which will see the new leader announced on September 25.

Nominations by members of the Parliamentary Labour Party will open on Monday.

So far just two candidates - David Miliband and his brother Ed - have declared their intention to enter the race.

The announcement sets the stage for a lengthy election campaign over the summer, culminating at the party's annual conference in Manchester.

Acting leader Harriet Harman, who took over following Gordon Brown's resignation last week, said she expected to see a "very dynamic campaign".

"It is going to be a very important opportunity for us to reflect on the result of the general election, to renew the Labour Party and to re-engage with the British people," she said.

She said the party would be actively encouraging new members to sign up so they can have a vote in the election.

"We're asking people to join us and to help shape the progressive future of this country by joining the Labour Party so that they too can play their part in this great election campaign," she said.

Under the timetable agreed by the national executive committee, candidates will have until Thursday May 27 to get the required 33 nominations by Labour MPs to enter the contest.

Hustings will be held during June and July and balloting will run from August 16 to September 22.

Labour MP John McDonnell accused the party hierarchy of attempting to "fix" the election process by "drastically curtailing" the nomination period to four days from next Monday.

The Hayes and Harlington MP, who unsuccessfully tried to stand against Gordon Brown when he became Labour leader, said the process was biased towards the Labour hierarchy's favoured candidates, claiming it largely excluded the possibility of other candidates coming forward to secure sufficient nominations.

Mr McDonnell said he was trying to attract enough nominations to stand in the leadership election.