Sir Gavin Williamson faces a series of inquiries into his conduct as fresh allegations emerged about his “unethical and immoral” behaviour.

No 10 is carrying out a fact-finding exercise following claims that Cabinet Office minister Sir Gavin told a senior civil servant to “slit your throat”, while the Tory party and Parliament’s bullying watchdog are looking into allegations made by former chief whip Wendy Morton.

Pressure continued to mount on Sir Gavin as his former deputy Anne Milton alleged he used intimidatory and threatening tactics while he was chief whip.

And the senior civil servant who claims to have been bullied by Sir Gavin when he was defence secretary has reportedly submitted a formal complaint to Parliament’s Independent Complaints and Grievance Scheme (ICGS).

Prime Minister Rishi Sunak’s decision to give a Cabinet-level role to the twice-sacked minister has led to questions about his judgment from critics.

No 10 said on Tuesday that Mr Sunak still maintains confidence in his ally, but indicated the Prime Minister would act if necessary.

In the latest disclosures, former deputy chief whip Anne Milton accused Sir Gavin of seeking to use an MP’s financial difficulties as leverage against them and sending an expletive-laden email about a female civil servant.

Ms Milton, who was deputy chief whip from May 2015 to June 2017, described his behaviour as “unethical and immoral”, claiming: “I think he feels that he’s Francis Urquhart from House Of Cards.”

Ms Milton, who was stripped of the Tory whip during the Brexit rows in 2019 and subsequently lost her seat, told Channel 4 News: “I got the impression that he loved salacious gossip, and would use it as leverage against MPs if the need arose.”

She told the broadcaster that Sir Gavin had a rant about civil servants in 2016 in response to a female official asking why a minister had to change travel plans for a vote.

“Always tell them to f*** off and if they have the bollocks to come and see me,” he said in an email, according to Ms Milton.

“F****** jumped up civil servants.”

She said that when the whips’ office gave some financial assistance to an MP, Sir Gavin told her that when she handed over the cheque she should make sure “he knows I now own him”.

She questioned Mr Sunak’s decision to give Sir Gavin a ministerial job, saying: “I think (at) best it was probably a bit naive. I don’t know that there are many people that would hang out the bunting to see Gavin Williamson back in government.”

The claims by Ms Milton follow allegations that Sir Gavin clashed with a civil servant while he was defence secretary.

Sir Gavin denied the official’s allegation of a campaign of bullying but did not deny making the remarks, including telling the civil servant to “jump out of the window”.

The Guardian, which first reported the allegations, said a complaint had now gone to the ICGS.

In a statement, the complainant said they had an “incredibly difficult period” working for Sir Gavin at the MoD and that the alleged bullying had had “an extreme impact” on their mental health.

Downing Street is understood to be undertaking a fact-finding exercise and considering how to respond to the allegations.

The Prime Minister’s official spokesman said: “Those are serious allegations that have come in.”

In a statement following the Guardian report, Sir Gavin said: “I strongly reject this allegation and have enjoyed good working relationships with the many brilliant officials I have worked with across Government.”

Meanwhile the PA news agency understands that former chief whip Ms Morton has referred her complaint to Parliament’s bullying watchdog, while an internal Tory party inquiry is ongoing.

Mr Sunak’s spokesman indicated he would not feel the need to wait until the resolution of existing investigations to act if the circumstances demanded it.

“Obviously he would act if and when he felt it was appropriate to do so,” the spokesman said.

Sir Gavin’s newly-revealed ministerial responsibilities include the Geospatial Commission, the Government Communications Service and the “Great Campaign” to promote the UK.

“After a week of appalling allegations about intimidatory behaviour towards colleagues, the Prime Minister has rewarded Williamson by giving him authority over huge swathes of the civil service,” deputy Labour leader Angela Rayner said.

The Prime Minister has been coming under sustained pressure over his decision to bring his ally back into Government despite knowing about the  complaint made by Ms Morton.

The Times, which first disclosed that she has referred her complaint to Parliament’s Independent Complaints and Grievance Scheme, said she made the move over fears of a “whitewash” by the Conservative Party.

In a series of texts peppered with swear words, Sir Gavin accused Ms Morton of seeking to “punish” MPs out of favour with then-premier Liz Truss by excluding them from the Queen’s funeral, warning: “There is a price for everything.”

The Liberal Democrats demanded an independent inquiry into Sir Gavin’s conduct so the Tories do not “mark their own homework”.

Sir Gavin, who was knighted after being nominated for the honour by Boris Johnson earlier this year, is a divisive figure at Westminster, where he is viewed with suspicion by many Tory MPs because of his reputation as an inveterate plotter.

He was sacked first by former PM Theresa May as defence secretary in 2019 for leaking details of a National Security Council meeting, and then by Mr Johnson as education secretary over the Covid-19 A-levels debacle.

However, he was regarded as a key figure in Mr Sunak’s campaign over the summer to become party leader.