The Sun claimed a "World Exclusive" yesterday when it published the findings of the Hutton Report before they were publicly available.
It was reported today in The Guardian that The Sun secretly acquired a copy of the report, which was produced under the tightest security at private printers. Trevor Kavanagh, The Sun's political editor and source of Wednesday's Hutton scoop, has only said that he received his information via telephone, refusing to divulge any details about the mole's identity.
He told The Independent: "There's no way if there is a police inquiry or any other sort of inquiry that we will reveal our source."
The law lord has asked Martin Smith, solicitor to his inquiry, to investigate who had access to the report in advance of publication to narrow down possible sources of the leak.
Blair has said he expects further action to be taken by the BBC in the wake of its criticism in Lord Hutton's report, which last night saw chairman Gayvn Davies resign.
The report cleared the government of "sexing up" its Iraq weapons dossier with unreliable intelligence and accused the BBC of "defective" editorial controls stemming from defence correspondent Andrew Gilligan's broadcasts on the 'Today' programme.
According to a Blair spokesperson, the government did not consider BBC director-general Greg Dyke's apology sufficient.
Blair's spokesman said: "The Prime Minister believes that the BBC will want to consider very seriously the profound criticisms from Lord Hutton about the reporting, the editorial control and management and the way the BBC governors themselves responded."
He added: "I think the BBC will have a very fair idea of what we are talking about."
In an immediate response to Hutton, Dyke admitted errors had been made over the BBC's coverage of the weapons of mass destruction dossier, but did not go so far as apologising.
"The BBC does accept that certain key allegations reported by Andrew Gilligan on the 'Today' programme on May 29 last year were wrong and we apologise for them. However, we would point out again that at no stage in the last eight months have we accused the Prime Minister of lying and we have said this publicly on several occasions," Dyke said.
The BBC's board of governors is today locked in a crisis meeting with a statement expected soon.
Lord Hutton himself has been called to appear before MPs on the administration select committee to give evidence on conducting a probe into the role of inquiries in government.
Chairman Tony Weight said that while they would not "revisit the facts of conclusions of Lord Hutton's report, this is an opportunity to learn from it".
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