The BBC will present fresh details about how the Iraqi weapons dossier was allegedly "sexed up'' by Downing Street and accuse Alastair Campbell of giving "inaccurate'' evidence to the official inquiry into the affair.
Publication of the claims, in the next 48 hours, will reignite the unprecedented row just as the Blair Government appears keen to damp it down. According to senior sources, the corporation has decided at the highest level not to give in to the relentless pressure from the Government.
Journalists and officials at the BBC have spent the weekend poring over the testimony given by Mr Campbell to the Foreign Affairs Select Committee.
According to the sources they have discovered "inaccuracies and inconsistencies'' in what the Prime Minister's communications chief told MPs. Andrew Gilligan, the BBC reporter who has been the focus of government attacks, will produce further information on how the intelligence services were supposedly pressured by Mr Campbell about the "45-minute threats'' posed by Saddam Hussein, which appeared in the first Downing Street dossier last September.
An investigation is under way, allegedly at the behest of Number 10, to hunt down Mr Gilligan's source.
Mr Gilligan, the defence and diplomatic correspondent of Radio 4's Today programme, has told Richard Sambrook, the head of news at the BBC, the identity of his informant. Greg Dyke, the director general, has been given details of the source but not his name.
Sources within the intelligence services have indicated that they will be "combative'' if the Government attempts to start a witch-hunt to find out those responsible for leaks to a number of journalists about the unhappiness within the services over how intelligence on Iraq was manipulated.
The hierarchy at the BBC is also ready for a prolonged confrontation with Downing Street over the affair. Both Mr Dyke and Gavyn Davies, the chairman of the board of governors, have links with New Labour. Taking on the Government at this stage is seen as a measure of their independence, according to BBC sources.
Mr Gilligan, with the backing of the BBC, has announced that he is ready to sue Phil Woolas, the deputy leader of the House of Commons, over the allegation that he misled the Foreign Affairs Select Committee. The BBC reporter had said he will proceed to sue Mr Woolas, who made the allegations in a letter to Mr Gilligan, which was also given to the media, unless he gets a retraction and an apology.
Unlike the accusations made against Mr Gilligan by Mr Campbell, Mr Woolas's remarks are not covered by parliamentary privilege.
Although Mr Gilligan has his critics within the BBC, the general consensus appears to be that the corporation should not back down in the confrontation with Number 10. A senior source said: "We shall let the public make up its own mind about Alastair Campbell when we present an analysis of his evidence."
Three former Beeb men lead attack on corporation
The Government's fierce attacks on the BBC over allegations that Downing Street "sexed up" a dossier on Iraqi weapons have been led by three former BBC journalists who now work for the government.
Phil Woolas, the deputy leader of the Commons, is being threatened with legal action by Andrew Gilligan over his claim that the BBC defence correspondent may have misled the inquiry by the Commons Foreign Affairs Select Committee. Mr Woolas is a former assistant producer on BBC2's Newsnight programme, and has battled with Jeremy Paxman, its presenter, over the issue.
The most explosive clash was on Saturday when Ben Bradshaw, a former BBC Radio 4 reporter who is now an Environment minister, locked horns with John Humphrys, the presenter of Radio 4's Today programme.
The third ex-BBC man is Tom Kelly, Tony Blair's official spokesman, who used a press briefing last week to list 12 questions the BBC should answer about its story. Mr Kelly, whose boss is Alastair Campbell, started his career with the BBC, holding several senior posts in Belfast and London.
Lord Birt is believed to have encouraged the close links with Labour as part of a campaign to protect the licence fee. Several other ex-BBC staff have links to Downing Street.
The BBC's claims that it is even-handed will receive some backing tomorrow when Theresa May, the Tory chairman, meets BBC bosses to complain of anti-Tory bias.