Michael Meacher has announced that he will run for leader of the Labour party when Tony Blair stands down.
Mr Meacher, the MP for Oldham West and Royton, was a minister from 1997 to 2003, and is from the left of the party.
He has consistently voted for gay rights legislation.
The BBC reports that he is confident he can get the support of the 44 Labour MPs required to get on the ballot.
Mr Meacher has been a vocal dissenter over the government’s determination to renew the Trident nuclear weapons system.
He has also urged for more action on climate change.
However, other Labour MPs have cast doubts on his ability to beat Gordon Brown and become Prime Minister.
“Michael Meacher is a major figure on the British political scene, yet the majority of people I have spoken to, who came into Parliament in the last six or seven years, just said: ‘Who?’
“They didn’t know who he was,” Stephen Pound, the MP for Ealing North, told the BBC.
Mr Meacher, an MP since 1970, was a shadow cabinet member and prominent Labour figure during the party’s wilderness years.
However, when the party finally regained power after 18 years of opposition, he was not invited into Tony Blair’s cabinet.
His candidacy is another sign that the Labour party may drift to the left once Mr Blair and Deputy Prime Minister John Prescott leave office.
They are expected to stand down in June.
Another left-wing MP, John McDonnell, has said he will challenge Gordon Brown for the leadership.
There have been persistent rumours that a more “Blairite” candidate will enter the race.
Home Secretary John Reid is often mentioned as a contender, as is Environment Secretary David Miliband.
The candidates for deputy leader have all been expressing a desire to renew the Labour party.
Front runners have been openly critical of some aspects of Mr Blair’s leadership.
Northern Ireland Secretary Peter Hain, International Development Secretary Hilary Benn and Constitutional Affairs minister Harriet Harman are declared candidates.
Education Secretary, Alan Johnson, has had his candidacy for the deputy leadership of the party endorsed by a string of ministers.
Backbench MP Jon Cruddas is also running for Mr Prescott’s job.
He is busy touring the country with a message of grassroots renewal, and could have strong appeal to disaffected party members.
Labour party chairman Hazel Blears is also expected to announce her candidacy for the deputy job soon.
The elections of a leader and deputy are one of the few real democratic processes left in the Labour party.
They will probably take place five weeks after Mr Blair announces his intention to go.
Any MP who wants to stand needs the backing of 12.5% of Labour MPs. At present that means 44 endorsements.
The party uses an electoral college to elect its leadership, split three ways between the MPs and MEPs, the party membership and members of affiliated unions. That means over a million people will get a vote.
Any candidate that gets 50% or more of the vote wins outright, otherwise further elimination ballots will be held.