Mr Blair will say the Conservatives have no strategy for government

Mr Blair acknowledged, weeks before the local elections, that the Tories have become a more effective opposition.

But he said Mr Cameron had failed to find a "strategy for government" and had made "misjudgements" on issues like ID cards and health service reform.

But Mr Cameron said it was "rather sad" that after ten years as PM Mr Blair was having to "resort to personal attacks".

The Tory leader, during a visit to south west England, said the reason the party was doing well in opinion polls was because it was "behaving like a government".

This was shown by backing things like Trident renewal because it was "right for the country" rather than "playing politics".

In his speech in his own Sedgefield constituency, Mr Blair, who has seen off three Tory leaders during his 10 years in power, said Mr Cameron had made his party "better now at the tactics of using the media and Parliament to harry the government".

Tactics learnt

But, he said, there was a big difference between learning the tactics of opposition, and coming up with a strategy for government.

And he said: "Every time they are called on to make a big judgement call on policy they misfire... they charge off in any direction which the popular bugle sounds."

Opinion polls over the past few months have consistently suggested that Labour are trailing the Conservatives, with a clear picture of voter sentiment due to be delivered in the Scottish Parliament, Welsh assemby and English local elections on 3 May.

John Major has been out there saying how David Cameron will win the next election... he's not going to Tony Blair

But Mr Blair sought to rally activists by saying it was "obvious the Tories are beatable at the next general election" and that Labour was the best party to lead the UK through the next decade.

Mr Blair's speech follows Sir John Major's comments on Thursday, in which he said Mr Cameron had the political stardust to succeed electorally- and attacked Mr Brown's record as chancellor.

Mr Brown is the front-runner to succeed Mr Blair as Labour leader - and consequently as prime minister - after he announces his resignation, which is expected shortly after the May elections.

1997

Sir John accused the chancellor of wrecking private pensions and introducing a tax credit scheme which had imploded and caused distress to many families.

And he said the chancellor could not "shuffle off" responsibility for what he described as "Labour's failures".

Mr Blair responded to those comments at the start of his speech, saying: "John Major has been out there saying how David Cameron will win the next election.

"I'm going to tell you that he's not going to. I would point out what happened in the 1997 election but that would be cruel."