The Government went to extraordinary lengths to gag Dr David Kelly because of fears that he would expose fundamental flaws in its case for war.
Documents released yesterday by the Hutton inquiry into the scientist's death reveal that the Ministry of Defence was even prepared to block a police investigation into a secrets leak.
Under the plan, Scotland Yard's Special Branch was to be prevented from interviewing Dr Kelly and anyone else who had discussed his doubts about Iraq's alleged weapons of mass destruction.
A confidential memo between two senior security officials in the MoD shows the extent to which the Government was prepared to go in its efforts to silence Dr Kelly.
Ian Barrow, of the Directorate of Safety and Security, wrote to John Cochrane of Defence Security - after discussing the matter with the MoD's director of personnel, Richard Hatfield: "We are to resist any attempt by the police to interview Kelly or anyone else who has interviewed him."
The intervention came during a top-level investigation into secret documents relating to Saddam Hussein and al-Qa'ida, which had been passed on to the BBC journalist Andrew Gilligan.
The memo went on to say that the police should be stopped from interviewing Dr Kelly "on the grounds that this should be outside the scope of MPSB [Metropolitan Police Special Branch] support for the inquiry into the ... document leak".
The newly released papers also show that Geoff Hoon, the Secretary of State for Defence, pressurised the Intelligence and Security Committee not to question Dr Kelly about his views on the Iraq weapons dossier.
In a letter to the committee chair, Ann Taylor, Mr Hoon said: "I presume Dr Kelly will be questioned only on the matters which are directly relevant to the claims made by Andrew Gilligan and not the wider issue of Iraqi WMD and the preparation of the dossier."
The Hutton inquiry has already heard that Mr Hoon sought to place similar restrictions on the investigation carried out by the Commons Foreign Affairs Committee (FAC) when they called Dr Kelly as a witness.
Documents released last night by the Hutton inquiry also show that Alastair Campbell, Downing Street's director of communications, urged Tony Blair to become "more combative" in dealing with critics over Iraq.
Among the hundreds of previously undisclosed documents released on the inquiry's website is a lengthy briefing note from Mr Campbell to the Prime Minister, advising him how to deal with the failure of Britain and the United States to find weapons of mass destruction in Iraq.
"The current frenzy flows from the fact that ... nothing new has been found," Mr Campbell writes. "Everything stems from that, so tomorrow is in part about saying as much as you can about the process towards discovery."
As part of the "more combative approach", Mr Campbell suggests that the Prime Minister tell Parliament that "the joy on the faces of the children I met [in Iraq] tells me we did the right thing".
A second note from Mr Campbell urges Mr Blair to allow him to give evidence to the FAC because of his role in chairing a key committee involved in compiling the Government's dossier on Iraqi weapons.
An email also released last night calls into question Mr Campbell's evidence to the inquiry last week on another issue: the way Dr Kelly's name became public. After the MoD issued a press release saying that an unnamed official had admitted meeting Mr Gilligan, newspapers were seeking the name of his contact.
Mr Campbell told the inquiry that he felt it was inevitable that the name would come out, "but I did not do anything to bring that about".
On 8 July, however, Mr Campbell was emailed by a journalist on The Times, Philip Webster, who said he had received a tip that Mr Gilligan's source "is a Foreign Office official (female) who is now in South Africa, having either left the FCO or been moved there for a diplomatic appointment. Do you recognise that?" Mr Campbell replied with one word: "Wrong."
Acknowledging that he had been spared a fruitless search, the journalist responded: "Thanks."
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