Four former Labour ministers came forward last night to blame Gordon Brown for creating a culture which allowed his former aide Damian McBride to draw up plans to smear senior Conservatives.
The ministers criticised his style of leadership, suggesting that Mr McBride was carrying out his wishes rather than acting as a freelance operator. They joined David Cameron in demanding an urgent shake-up of the Downing Street machine.
Mr Brown also faced the prospect of an embarrassing inquiry into the role of special advisers like Mr McBride. Labour MPs want the Public Administration Select Committee, which has looked into their work after previous controversies, to launch another investigation. "We have got to make sure that this sort of thing disappears once and for all and that politics becomes a serious and respected profession again," said Kelvin Hopkins, a Labour member of the committee.
David Cameron, who was one of Mr McBride's targets, said: "I do not know what Gordon Brown knew and when he knew it but what I do know is that he hired these people, he sets the culture, he is the leader and we need change in order to change the culture and stop this sort of nonsense."
While Mr Cameron's attack was expected, Mr Brown was left more wounded by the flak from his own side. Frank Field, a former welfare reform minister, made clear his criticism pre-dated Mr McBride's arrival on the political scene. "A necessary government information machine has been corrupted by a spin that seeks not to inform but control and, if needs be, destroy. And it has been in existence for over a decade," Mr Field said.
"Mr McBride thought he was doing his master's bidding – he wouldn't have done it otherwise. There are two sides to the Prime Minister's character – there is this very civilised, generous, informed side and there is this other side which is about controlling people. And I find it amazing that somebody who puts so much emphasis on controlling people was not more in control of Downing Street."
Mr McBride's activities "shine a searchlight on the paucity of the Government's programme", described as "vacuous". Mr Field said: "Labour MPs are left staring into the abyss."
Two Blairite former ministers, Stephen Byers and Alan Milburn, also broadened the attack on Mr Brown. Mr Byers, the former transport secretary, said: "To dismiss the incident as juvenile, which was the first reaction of Downing Street, totally missed the point and failed to recognise the extent of the hurt and offence caused. If there are people close to the Prime Minister who are thinking of fighting the forthcoming general election in a personal and dirty way, they should go, and go now."
Mr Milburn, the former health secretary, described the proposed website as "morally unacceptable" and said the row had inflicted huge damage on the Labour Party and on the Government.
"It is very, very important in my view that, as a consequence of the events of these last few days, that we end this sort of approach to politics, which demeans politics, is completely out of kilter with the culture of Labour politics – and that we end it once and for all," he said.
Charles Clarke, the former home secretary, said politics had been "debased" by the affair and that two Labour figures who discussed the proposed website with Mr McBride – Derek Draper and Charlie Whelan – should sever their links with the party's leadership.
Labour backbenchers are dismayed, with some describing the revelations as one of the darkest chapters in the party's history.
One said last night: "A colleague said to me, 'What would Clement Attlee have said about this?' The truth is he would never have surrounded himself with these people from the start."
Another Labour MP said: "I thought the stables had been cleaned out when Blair went. I hope now they will be cleaned once and for all, and we stop indulging in this kind of so-called politics."
Cabinet ministers rallied to Mr Brown's defence. Ed Miliband, the Climate Change Secretary, said the Prime Minister did not have a "dark side", adding: "He's not someone who thinks that the politics of innuendo is how you win elections."
Lawyers acting for Tom Watson the Cabinet Office minister – and a close ally of Mr Brown – issued a statement last night insisting he had "no involvement in or knowledge of" the Red Rag blog proposal.
Carter-Ruck Solicitors said complaints had been lodged with the Daily Mail and Mail on Sunday over reports they published alleging that Mr Watson had been involved.
Mr Brown has sent personal hand-written letters expressing regret to Mr McBride's targets. But the Tory MP Nadine Dorries dismissed the letter she received, saying it was intended simply to put Mr Brown in the clear.