Charles Clarke has been one of Gordon Brown's most persistent critics
Gordon Brown should consider quitting to stop Labour getting "hammered" at the next election, says former home secretary Charles Clarke.
He told the Evening Standard that without change Labour could be forced into opposition "for 10 to 15 years".
Mr Clarke suggested Mr Brown's "own dignity" should lead him to consider quitting, perhaps citing ill health.
Asked about the comments, the prime minister said: "I'm healthy and very fit. I run a lot to keep fit."
Speaking to BBC Radio 5 Live Mr Brown, who was named World Statesman of the Year by US human rights group the Appeal of Conscience Foundation on Tuesday, added: "I keep going and I've got a job to do."
The newspaper reported that Mr Clarke, who is due to give a speech later to the Progress pressure group, hoped rumours the prime minister might stand down, perhaps claiming poor health, would come true.
"I don't think Gordon will lead Labour into the next election. I think his own dignity ought to look to that kind of solution," he said.
The former cabinet minister, who is a long-time critic of Mr Brown, also criticised colleagues who he said had already given up on the next election.
"They say prepare to battle in 2015, make sure the policies and leader are in place'," he said.
"I understand that, but there will not be a 2015 if we get hammered in 2010. And on current show, we will be."
Chief Secretary to the Treasury Liam Byrne told the BBC it was "not a new criticism" from Mr Clarke.
"I don't think anyone will be in the dark about what Charles thinks of Gordon Brown. He has made these points a number of times before," he said.
"Actually, we don't have a better leader of our party, or of our government, or of our country right now."
Mr Byrne said voters were more worried about important issues like getting the economy moving.