Theresa May's closest aide has quit and Education Secretary Michael Gove has been forced to apologise as the Prime Minister attempted to end the damaging dispute at the heart of his Cabinet.
The Home Secretary's special adviser Fiona Cunningham resigned following the investigation ordered by David Cameron into the briefings and counter-briefings which overshadowed the launch of the Government's programme for the final year of the coalition.
Mr Gove wrote to apologise to a senior Home Office official and the Prime Minister "in acknowledgement of his role" in the row, which saw the Education Secretary's camp and Mrs May's side publicly feuding over the way Islamist extremism was tackled.
The Prime Minister was understood to be "deeply frustrated" at the row and particularly the way it broke in The Times on the day of the Queen's Speech.
Mr Cameron was also forced to answer questions about the dispute while sharing a platform with Barack Obama at the G7 summit.
Ms Cunningham's resignation and Mr Gove's apologies follow an investigation by Cabinet Secretary Sir Jeremy Heywood, who was ordered to get to the bottom of the dispute by the Prime Minister.
Quotes attributed to a Department for Education source in The Times detailed Mr Gove's concerns about the Home Office's approach to tackling extremism and the attitude of Charles Farr, the director general of the Office for Security and Counter-Terrorism.
The source said: "Charles Farr always believed if extremists become violent we should deal with it. It has been characterised by others in government as just beating back the crocodiles that come close to the boat rather than draining the swamp."
But Mrs May's camp hit back, releasing a letter from the Home Secretary to the Education Secretary questioning his department's response to the Islamist "Trojan horse" allegations in Birmingham schools and a source said: "Why is the DfE wanting to blame other people for information they had in 2010? Lord knows what more they have overlooked on the subject of the protection of kids in state schools? It scares me."
Indicating that Mr Gove and Ms Cunningham were responsible a Downing Street spokesman said: "In relation to unauthorised comments to the media about the Government's approach to tackling extremism and the improper release of correspondence between ministers, the Prime Minister has received the Cabinet Secretary's review establishing the facts behind these events.
"In acknowledgement of his role, today, the Secretary of State for Education has written separately to Charles Farr and the Prime Minister apologising for the original comments made to the Times newspaper. In addition, in relation to further comments to the Times, Fiona Cunningham has today resigned."
Ofsted is set to publish its reports on Birmingham schools at the centre of the claims about an Islamist takeover plot on Monday and Mr Gove will make a statement in the Commons.
No 10 said: "The Prime Minister has been deeply concerned by the allegations made about extremism and a number of Birmingham schools. The Government, through the Department for Education and Ofsted, has taken swift action to investigate these allegations since they emerged in late 2013.
"The Prime Minister is taking a specific interest in ensuring this serious matter is being dealt with effectively.
"The detailed findings of the investigations will be set out in Parliament on Monday by the Secretary of State for Education.
"The Prime Minister has made clear that he expects a robust response from all relevant organisations to any findings that confirm that the safety and learning of children in our schools have been put at risk.
"The Prime Minister has prioritised fighting all forms of extremism, including through setting up his Extremism Taskforce in the wake of the horrific killing of Lee Rigby."
Mr Gove had earlier denied that the row with Mrs May had damaged the Government or that he was considering his position over his department's handling of the Birmingham allegations.
Questioned about the spat at a public appearance for the first time since details of the clash emerged, Mr Gove responded in one word: "No."
Labour said the developments were an indication of "chaos at the heart of the Government's efforts to tackle extremism" and said there were still unanswered questions about Mrs May's role.
Shadow home secretary Yvette Cooper said: "Theresa May's closest adviser has resigned for inappropriate release of ministerial correspondence yet the letter to the Education Secretary was signed and sent by the Home Secretary on the same day it was leaked to newspapers. Was this letter written in order to be leaked and did the Home Secretary authorise its inappropriate release?
"More importantly the Government now needs to ensure that all departments are working together on an agreed joint strategy to work with communities on preventing extremism.
"Tackling extremism is vitally important and departments should be working together to combat it - what is clear is that hasn't been happening as two Cabinet Ministers instead waged a briefing war. The parents, pupils and people of Birmingham and the whole country deserve better than that."
Shadow education secretary Tristram Hunt said: "Michael Gove should be apologising to pupils and parents, not David Cameron. He was warned of the problems in Birmingham four years ago.
"Michael Gove can no longer seek to distance himself from the mess that he has created. He must explain in full what he knew about the warnings he was given in 2010.
"By refusing to take action on the lack of local oversight of our schools he is leaving pupils exposed to falling standards and risk."