Mr Clarke has been critical of Mr Brown on several occasions
Labour is "destined to disaster" and "utter destruction" at the next election if it does not change, former home secretary Charles Clarke has said.
But there was not any "Blairite plot" to oust Prime Minister Gordon Brown, he writes in the New Statesman magazine.
He says comments by Foreign Secretary David Miliband had been misrepresented by the "Brown political briefing team".
Mr Clarke, sacked as home secretary 2006, said there was a "deep and widely shared concern" among Labour MPs.
In his article in this week's New Statesman, he calls Mr Brown's decision - in his last Budget as chancellor in 2007 - to abolish the 10p rate of income tax "disastrous and unfair".
The comment comes after the government announced several new economic policies - dubbed by many as the start of a "relaunch" for the prime minister.
'Not a guide'
Mr Clarke, MP for Norwich South, said Tony Blair had been an "outstanding" prime minister, but added: "Blairism as a concept offers little by way of rescue. It is certainly not a guide to action.
Blairite" (even "über-Blairite") is a lazy and inaccurate shorthand
"Equally, however, it is inaccurate and misleading to dismiss as some kind of Blairite rump those who fear that Labour's current course will lead to utter destruction at the next general election."
He said there was "no Blairite plot, despite rumours and persistent newspaper reports".
"There is, however, a deep and widely shared concern - which does not derive from ideology - that Labour is destined to disaster if we go on as we are, combined with a determination that we will not permit that to happen."
The former home secretary goes on to say the term "Blairite" (even "über-Blairite") is a lazy and inaccurate shorthand. It is intended not to illuminate but to diminish, marginalise and insult.
"It was, for example, the stock phrase used by the Brown political briefing team to traduce David Miliband's Guardian article in early August."
New Statesman political editor Martin Bright
That article warned against "fatalism" ahead of the next general election and failed to mention Mr Brown once when discussing Labour's future.
This was interpreted by Labour's opponents as setting the platform for a possible future leadership bid, which Mr Miliband denied.
Mr Clarke, seen as a leading Blair supporter, has been critical of Mr Brown on several occasions.
In January, he accused Labour of suffering from a "debilitating" lack of direction under him.
But senior Labour backbencher Helen Jones said Mr Clarke was not representative of most Labour MPs.
She said: "This week our Labour government has started to outline further initiatives to help hard working families - help for first time buyers, and a £120 tax cut this month which will help pay the bills.
"That's the sort of thing the public wants to hear from all Labour MPs.
"Charles is not speaking for the bulk of the parliamentary Labour Party."
BBC political correspondent Jo Coburn said this was not the first time Mr Clarke had publicly criticised the prime minister, but that he had used very strong language.
"This re-opens the whole question about Gordon Brown's leadership and will reignite the debate amongst Labour MPs as to whether there is a need to change the man at the top," she said.
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