Labour's future as a viable party of government is under threat as it tears itself apart over the contest to elect a new leader, Lord Mandelson has suggested.
The former Cabinet minister followed Tony Blair in issuing a warning to the party over its future after radical left-winger Jeremy Corbyn surged ahead in a shock poll to become the front-runner to take the top job.
After a bruising day of recriminations the architect of its most successful electoral era said Ed Miliband's tenure had left Labour with a "terrible legacy".
Lord Mandelson told The Times: "Those of us who stayed and fought to save the Labour party in the 1980s will be experiencing a growing sense of deja vu.
"The last five years have left us with a terrible legacy to overcome with the existence of the Labour party as an effective electoral force now at stake."
Mr Corbyn took the lead in a shock poll yesterday prompting suggestions that one of the candidates should now withdraw from the race to ensure he is defeated.
Leadership hopeful Andy Burnham made the surprise admission that he would serve in the shadow cabinet if the veteran MP takes the party's top job.
Fellow contender Yvette Cooper left the door open to remaining on the front bench but moderniser Liz Kendall ruled out taking a position with a flat "no".
During a leadership hustings on LBC, she warned that a Corbyn win would put the party out of power for "a generation".
"I think it would be disastrous for the party, it would be disastrous for the country, we'll be out of power for a generation," she said. "I don't want to be a party of protest and I wouldn't be able to stop myself from making that case."
Pressed whether he would take a shadow cabinet position under Mr Corbyn, Mr Burnham said: "I would. I would serve the Labour Party at any level it asked me to serve the Labour Party."
Ms Cooper said: "I'd be torn because the truth is I think it would be quite hard given the differences in terms of policy.
"The other thing is I don't think you should walk away from the Labour Party."
The debate came at the end of a tough day for Labour as its factions clashed over the future direction it should take following its woeful general election performance.
Mr Blair issued a stark warning to the party not to repeat the mistakes of the 1980s which consigned the party to 18 years in opposition.
The former prime minister said a shift to the left after the party's crushing general election defeat would be to treat voters as if they were "stupid".
He derided Mr Corbyn as the "Tory preference" and said the party could not regain power if it was simply a "platform for protest" against cuts.
"It would not take the country forwards, it would take it backwards," he said. "This is why when people say 'My heart says I should really be with that politics' - get a transplant."