Theresa May is set to lay down the law with senior colleagues on the need to keep Cabinet discussions private, after a series of vicious leaks targeting Chancellor Philip Hammond.
The Prime Minister will use Tuesday's regular Cabinet meeting to "remind" ministers that they should maintain silence about the content of meetings and focus on their job of delivering for the public, Mrs May's official spokesman told reporters.
The attempt to instil Cabinet discipline comes after a series of newspaper headlines about Mr Hammond's comments at last week's Cabinet, culminating in a Daily Telegraph front page story quoting an unnamed minister accusing the Chancellor of trying to "f*** up" Brexit.
Mrs May's spokesman declined to discuss the content of the leaks, but told reporters at a regular Westminster media briefing: "Of course, Cabinet must be able to hold discussions of Government policy in private and the Prime Minister will be reminding her colleagues of that at the Cabinet meeting tomorrow."
The infighting came as the second round of EU withdrawal talks got under way in Brussels, with Brexit Secretary David Davis and European Commission chief negotiator Michel Barnier saying that officials will focus on the issues of citizens' rights, borders and the UK's financial settlement in discussions due to last four days.
Soon after the formal opening of discussions, Mr Davis set off back to London, leaving officials to get on with negotiations until he returns to Brussels on Thursday for a press conference with Mr Barnier.
The PM's spokesman said he was not aware of any inquiry into the source of the leaks from last week's Cabinet.
According to newspaper reports, Mr Hammond was slapped down by the Prime Minister for saying that women could "even" become train drivers - a claim he denied. And a separate report said that he had told colleagues that public sector workers were overpaid compared to those in the private sector.
The Chancellor used a TV appearance on Sunday to accuse Cabinet rivals of trying to undermine his agenda for a "softer" business-friendly Brexit prioritising jobs and the economy.
But one unnamed Cabinet minister was reported to have hit back, claiming Mr Hammond was part of an attempt by "the Establishment" to prevent Britain ever leaving the EU.
The Daily Telegraph quoted the minister as saying: "What's really going on is that the Establishment, the Treasury, is trying to f*** it up. They want to frustrate Brexit."
The row was being seen as further evidence of Mrs May's weakness after seeing her Commons majority wiped out in last month's general election.
The PM's spokesman made clear she intends to assert her authority by telling colleagues to focus on their departmental responsibilities.
"She will be reminding them of their responsibilities and making the point that ministers across Government need to be focused on getting on with delivering for the British public," he said.
"I'm not going to get into speculation of who said what where and when. I'm simply saying that Cabinet must be able to hold its discussions on Government policy in private, and the PM will remind her colleagues of that at tomorrow's meeting."
Asked whether Mrs May rejected the unnamed minister's claim that the Treasury was trying to undermine Brexit, the spokesman said: "I'm not getting into anonymous quotes. What I would say is that the Government is all working together to deliver Brexit, which delivers on the will of the British people."
Transport Secretary Chris Grayling attempted to play down suggestions of Cabinet splits over Brexit and criticised those who have been briefing about its meetings.
"I don't see these great divisions that are suggested to me in the Sunday newspapers and I have to say I think all of this is somewhat overplayed," he told BBC Radio 4's Today programme.
Mr Grayling said the suggestion that there were "profound and fundamental differences" between Cabinet ministers on Brexit were "a bit exaggerated", but admitted: "We're not a group of clones, we have discussions around the Cabinet table and outside Cabinet, we debate issues, we decide what's right and then we get on with it.
"I'm very clear that the Cabinet and the party are united behind Theresa May, united in determination to get the right deal for the country in the Brexit negotiations and to make sure we continue the economic progress we've made."
Kicking off the second round of Brexit talks in Brussels, Mr Davis said: "We are now getting into the substance of the matter.
"It's four categories really. The issue of citizens' rights, the issue of finance, the issue of separation issues and, of course, separately, Northern Ireland.
"For us it's incredibly important we now make good progress. That we negotiate through this and identify the differences, so that we can deal with them, and identify the similarities so that we can move forward.
"And now it's time to get down to work and make this a successful negotiation."
Mr Barnier said: "I look forward to our negotiations this week. We'll now delve into the heart of the matter.
"We need to examine and compare our respective positions in order to make good progress.
"As you know, our negotiating groups will work on citizens' rights, on the financial settlement and other separation issues.
"David and I will be in contact throughout the week. Rendezvous to take stock together on Thursday."
Conservative former deputy prime minister Lord Heseltine said the "very distressing" infighting within the party's upper echelons was a sign of Mrs May's lack of authority.
The Tory peer said he believed the leaks came from "a leading Brexiteer" and was sure that the PM would know who it was. Asked if Mrs May should sack those responsible, he said: "She would if she could."
But he told BBC Radio 4's World At One: "She can't sack leading Brexiteers because she has no authority, so you have an enfeebled Government."
Lord Heseltine added: "I think it's very distressing. I think that the chances are there will be a general election in two years and I don't see any sign of the Conservative Party focusing on how it wins that election."
He said that, in the Government's fragile condition, its best interests were to be "bold (and) forward-looking" and effectively dare the opposition to bring it down.
But he said he was "frightened" that any change in the leadership would simply mean a different prime minister persisting with Mrs May's "Brexit is Brexit" approach.
The EU was aware that "this is a Government without authority, this is a deeply divided Government", while Labour was in a position of being able to wait and see which way public opinion moves on Brexit before positioning itself to take advantage at the next election, he warned.
As talks opened in Brussels, Mr Davis and his team were photographed sitting without any papers opposite EU negotiators with stacks of papers on the table in front of them.
Liberal Democrat Brexit spokesman Tom Brake said: "We have less than 20 months of Brexit talks left, yet David Davis has skulked back to the UK after just half a day.
"He didn't have any position papers with him because this Government has no agreed Brexit position.
"This is a Government with no papers, no plan and no time for the most important negotiations of a lifetime.
"They are meant to be negotiating Brexit, but they can't even negotiate among themselves."
Scottish National Party Europe spokesman Stephen Gethins said: "It is staggering that on the day the Brexit Secretary begins the second round of negotiations with the EU, the increasingly distracted and divided Downing Street is briefing on internal Tory squabbles and leaks, rather than the key issues which clouded in uncertainty for over a year.
"Theresa May must get a grip and she must do so quickly."