By Tony O’Reilly-
Jason Stein, a special adviser to Liz Truss, is to face a formal investigation by the Propriety and Ethics Team, which is responsible for standards across government.
Conservative backbench MPs have expressed anger and disappointment about briefings from No 10 sources over the weekend.
Mr Stein previously worked for Ms Truss when she was chief secretary to the Treasury before he became a special advisor to Amber Rudd.
He also worked for Ms Truss during her Tory leadership campaign.
A Number 10 spokesperson said: “We don’t comment on individual staffing matters but the prime minister has made clear to her entire team that remarks attacking parliamentary colleagues are totally unacceptable and must stop.”
Sky News’s political editor Beth Rigby said it was “another crisis emerging for Liz Truss within her own team”.
The suspension was confirmed just before Ms Truss began her third session of Prime Minister’s Questions in the Commons as she battles to hold onto her premiership following Mr Kwarteng’s removal and reversal of most of her government’s mini-budget.
The PM made a public apology in the Commons as she faced questions from Labour leader Sir Keir Starmer for the first time since her economic plan was ditched by new Chancellor Jeremy Hunt.
“I have been very clear that I am sorry and that I have made mistakes,” she told MPs.
Asked about the suspension, Ms Truss’s spokesman refused to refer to Mr Stein by name but told reporters: “The prime minister has made it very clear that some of the briefings are completely unacceptable and must stop.”
This was a reference to briefings to newspapers from those around her who can speak on her behalf, which contained strong language.
Over the weekend, the Sunday Times reported that Ms Truss was of the view that the former Chancellor and Health Secretary Sajid Javid was “shit”.
Mr Javid had been seen by some as a possible replacement for Kwasi Kwarteng as chancellor, but Jeremy Hunt was picked instead.
Asked if Mr Stein had offered his resignation, a Conservative source said “that is not my understanding”.
Before joining Downing Street, Jason Stein used to work as a communications adviser to Prince Andrew.