The BBC's Nicholas Jones answers the question: "Does it matter what The Sun says?"

The paper's editor David Yelland said he wanted to start a debate about the issues surrounding the euro.

The paper devoted its entire front page on Wednesday to an editorial with a picture of the prime minister alongside the headline: "Is THIS the most dangerous man in Britain?"

The Sun claims: "He [Mr Blair] seems determined to scrap the Pound [sic] and take Britain into the European single currency.

"And that, we believe, will be the biggest gamble any Prime Minister has ever taken. The result could be disastrous for this country."

Murdoch 'had not seen paper'

Mr Yelland told the BBC the paper had acted because "we believe that Tony Blair is a very talented and probably one of the greatest prime ministers of the century and we believe there is a danger ... he could be taking us down the road that the vast majority of people are not convinced of."

Sun editor David Yelland explains the paper's stance on BBC Radio 4's Today programme

He added: "It is because of his ability to persuade people that he could be the most dangerous man in Britain, because he could be taking us into a common currency that I don't think there has been enough debate about."

Mr Yelland insisted the views expressed in the paper were his and that The Sun's proprietor, Rupert Murdoch, had not seen the paper.

He said: "He owns the paper, so of course he is in agreement with it."

The Sun claimed to have been instrumental in getting Mr Blair elected when it switched its support from the Tories before the general election.

It denies abandoning him now, saying: "The Sun backed him at the election because we believed he was the best man for the job. We still believe that.

"But our support ... did not give him a blank cheque."

Inside the paper, the headline "The Tone Danger" sits alongside a picture of Mr Blair wearing a mask to resemble the western hero known for his "Hi-ho Silver - Away" catchphrase.

Campbell: 'Self-obsessed media'

Downing Street has played down the significance of the article, saying The Sun is following its own agenda.

Alastair Campbell: on the record criticism of BBC

Alastair Campbell, the prime minister's official spokesman, criticised the BBC's coverage of the story.

Mr Campbell issued a brief statement saying: "The BBC's excited coverage of The Sun utterly confirms the point I was making yesterday about a media obsessed with itself.

"The Sun has a well-known position on the single currency and the fact that it restates it doesn't strike me as terribly newsworthy."

Mr Campbell said he thought the story was best left to the newspaper reviews the BBC broadcast.

He said: "I just wonder - is it the second most important thing happening in the world today? I cannot think it is."

The move coincides with the day the shadow Chancellor Francis Maude spells out the Tory view of the economic dangers and costs of joining the single currency.

Mr Maude said: "We think Mr Blair and Mr Brown are taking Britain on a route march for dogmatic reasons towards something which is full of risks.