Brown should resign

Mr Clarke told the BBC "many, many, many people" shared his concerns.

He spoke as Mr Brown prepares to continue his autumn fight back with a speech to business leaders.

Schools secretary and key Brown ally Ed Balls dismissed the attack as "Charles being Charles". Minister Phil Hope said Mr Clarke should "shut up".

Mr Clarke has a track record of criticizing Mr Brown and was one of only a handful of Labour MPs not to publicly back his bid for the premiership last year.

He has been touted as a potential leader himself, but he earlier ruled out a challenge to Mr Brown in an interview with BBC Radio 4's Today programme.

Asked if he would be prepared to stand against the PM as a "stalking horse" - to flush out more heavyweight challengers - he said: "I wouldn't do that myself - and I wouldn't counsel anybody else to do it either."

Speaking to BBC Political Editor Nick Robinson, he said he lacked the support for a bid himself but would "urge a leadership contest," adding there were "five or six people of quality" who would make good candidates.

Mr Clarke launched his latest salvo against the PM in an article for The New Statesman, writing that Labour faced "utter destruction at the next general election" if it continued on its current course.

He stressed that there was no "Blairite plot" against Mr Brown but there was a "deep and widely shared concern" in the party that Labour was heading for "disaster" coupled with a determination "that we will not permit that to happen".

Asked on Today what Mr Brown had to do, he said "establish his authority and set a very clear leadership direction".

And he said the government's performance must improve "significantly" or Mr Brown should "stand down as prime minister with honor and have a proper leadership election and address the proper issues".

Asked how long he gave Mr Brown, the former home secretary said: "I think it's a question of months really." Labour MPs have lined up to defend Mr Brown, with one of his closest allies, Ed Balls, telling GMTV: "It's not the first time Charles has made those kind of comments. I think it's Charles being Charles.

He is sabotaging the party.