One of Liz Truss's most senior advisers in No10 has been suspended pending an investigation, it is understood.
Special adviser to the Prime Minister Jason Stein will now face a formal probe by Whitehall's propriety and ethics team, according to the BBC.
Mr Stein previously worked on Ms Truss's leadership campaign and was a special adviser to the former cabinet minister Amber Rudd.
He was also hired as Prince Andrew's spin doctor but reportedly left the role in 2019 after his advice to reject a BBC Newsnight interview was ignored.
Ms Truss's press secretary said on Wednesday they would not "get into individual staffing matters" when quizzed on Mr Stein's suspension.
But they added: "The Prime Minister has made very clear to her team that some of the sort of briefings we have seen are completely unacceptable about parliamentary colleagues and they must stop".
Asked whether Mr Stein had offered his resignation, they added: "That's not my understanding".
The press secretary's comments come amid anger among some Tory MPs over anonymous briefings from government sources as the embattled Prime Minister clings to power.
The press secretary refused to confirm or deny reports that Tory MP Sajid Javid, who a No10 source branded "s***" in the Sunday Times, complained to Downing Street.
Five MPs have already publicly called for Ms Truss to resign, including Crispin Blunt who told her the "game is up" after she sacked Chancellor Kwasi Kwarteng and ripped up her economic agenda.
Just moments before Mr Stein's suspension was reported, Ms Truss again apologised to MPs over the economic turmoil.
The Prime Minister, who faced shouts of "resign" as she spoke, told them:"I have been very clear that I am sorry and that I have made mistakes."
"The right thing to do in those circumstances is to make changes, which I have made, and to get on with the job and deliver for the British people."
On Wednesday evening Ms Truss will also order Tory backbenchers to vote a measure on fracking her government is treating as a "confidence motion"
The move comes as Labour launches a bid to force a ban on fracking by giving the party powers to seize control of the parliamentary timetable next month.
Deputy Chief Whip Craig Whittaker told them it will be a "100% hard" three-line whip, saying: "This is not a motion on fracking. *This is a confidence motion in the Government.*
"We cannot, under any circumstances, let the Labour Party take control of the order paper and put through their own legislation and whatever other bits of legislation they desire.
"We are voting NO and I reiterate, this is a hard 3 line whip with all slips withdrawn."
Mr Stein has been contacted for comment.
