Speaking to ITV News, David Blunkett has told those criticising Ed Miliband to "get off your bum, and get out there and campaign."
The veteran MP - who has announced he is standing down - said: "My message to people who are chipping away at Ed Miliband: forget the idea that someone else is going to step forward or there's going to be some kind of peremptory election. There isn't.
"So get off your bum and get out there and campaign. Not for any individual but for the values we espouse."
Mr Blunkett added that if Labour were to lose next year's election they could be out of power for a very long time.
Ed Miliband said David Blunkett had been a "huge asset" to Labour and will be "hugely missed", after the former home secretary announced his decision to leave parliament.
"David Blunkett is a man whose commitment and determination have carried him to the highest positions in politics with one purpose: to serve the people of our country. He will be hugely missed," Mr Miliband said.
"He has been a friend to me during my time as leader. I have valued and counted on his advice and wisdom. Every Labour leader under whom he served would have said the same. He is Labour through and through.
"David can take great pride in all he has done to improve the lives of people in this country. He has been an amazing asset to the Labour Party and to Britain and I know he will continue to serve the country and the Labour Party with great distinction."
David Blunkett said Ed Miliband would want a "clear break from the past" if Labour won next year's general election, as he announced his decision to step down from Parliament.
Mr Blunkett, who will leave his Sheffied Brightside seat at the next general election, admitted to party members that standing down was his "most difficult political decision".
Next year will see 10 years on the backbenches, five in opposition.
Whilst I have been able to use the experience and the clout which came from having been a Cabinet minister for the benefit of the constituency in getting a hearing, contributing to policy and providing a voice for local people and for Sheffield at national level, it is clear that the leadership of the party wish to see new faces in ministerial office and a clear break with the past.
There does come a time when a fresh approach and the energy that goes with it outweigh other considerations, and I believe that for the party and for the constituency, as well as for me personally, that moment has come.
Jurors have been played furious voicemail messages left by former Home Secretary David Blunkett in the wake of false press claims about his relationship with a female friend.
The Old Bailey was played recordings from the autumn of 2005 in which the politician said he hoped whoever had leaked information to the media would "rot in hell".
The voicemails were left on the mobile phone of Sally Anderson, a former estate agent who befriended Mr Blunkett in 2005.
In one message left on Ms Anderson's phone, he said: "Someone very, very close has done a really phenomenal piece of work on destroying both our lives at this moment in time and it's vile."Whoever it is I hope they rot in hell."
It is claimed that the messages were illegally accessed on behalf of journalists at the now-closed tabloid the News of the World (NotW).
"Human nature is you get carried away, so we have to protect ourselves from ourselves. In Government you are pressed by the security agencies. They come to you with very good information and they say, 'You need to do something'.
"So you do need the breath of scepticism, not cynicism, breathing on them. You need to be able to take a step back.
"If you don't have this, you can find yourself being propelled in a particular direction."
He said a high-level review by specialists was the best way to update laws.
David Blunkett has become the latest senior Labour figure to voice concerns about the party's failure to get its message across and warned that Ed Miliband is unable to secure electoral success on his own.
The former home secretary appeared to compare the Labour leader to post-war prime minister Clement Attlee, who he said "wasn't the most vibrant" public performer.
Mr Blunkett said the Labour leader needed to be "on the ball" at all times and suggested the party must begin setting out policies soon to give voters a clear idea of its vision.
He told BBC Radio 4's Today programme, "I would accept what's been said over the last few weeks, including the article by John Prescott on Sunday, that we need to work out how to get a higher profile in circumstances where it is very difficult to get a hearing."