Sir Gavin Williamson has quit Rishi Sunak’s Cabinet after conceding that allegations about his conduct had become a “distraction”.

The former Cabinet Office minister said he had decided to “step back from Government” while the complaints process into his conduct is carried out, vowing to “clear my name of any wrongdoing”.

The decision to quit follows allegations he sent expletive-laden messages to former chief whip Wendy Morton complaining about being refused an invitation to the Queen’s funeral, claims he bullied a former official at the Ministry of Defence and an accusation of “unethical and immoral” behaviour while he was chief whip.

Sir Gavin said there was an ongoing complaints process “concerning text messages I sent to a colleague” - a reference to Ms Morton’s complaint.

He said: “I am complying with this process and I have apologised to the recipient for those messages. Since then, there have been other allegations made about my past conduct. I refute the characterisation of these claims, but I recognise these are becoming a distraction for the good work this Government is doing for the British people.

“I have therefore decided to step back from Government so that I can comply fully with the complaints process that is underway and clear my name of any wrongdoing.”

The flurry of accusations against Sir Gavin had triggered a series of investigations by the Tory party, the Commons bullying watchdog and an informal fact-finding exercise by No 10.

The Prime Minister appointed Sir Gavin to the Cabinet Office knowing he was the subject of an official party complaint, has now been reported under a new procedure.

His resignation came just hours after Downing Street insisted Mr Sunak still had full confidence in the minister.

Former Chief Whip Wendy Morton asked the Parliament’s Independent Complaints and Grievance Scheme to look into the matter after The Times reported she feared a “whitewash” by the Tory party.

Sir Gavin sent Ms Morton a series of expletive-laden texts accusing her of trying to “punish” MPs out of favour with then PM Liz Truss by excluding them from the Queen’s funeral. He said Ms Morton was trying to “f*** us all over”, adding: “There is a price for everything”.

Scottish Tory leader Douglas Ross has said he would have sacked any of his front bench who used such language to a colleague.

Mr Sunak said the language was “not acceptable”, but No10 later insisted the Prime Minister still had full confidence in him.

Ms Morton’s referral to the Commons watchdog coincided with yet more allegations of bullying and intimidation by Sir Gavin.

The Guardian reported that in his former role as Defence Secretary, he told a senior official to “slit your throat” and “jump out of the window”.

The paper said the official, who later left government, complained to the MoD’s head of human resources about the alleged incidents.

Former deputy chief whip Anne Milton last night accused Sir Gavin of behaving in an “unethical and immoral” and “shocking” manner during his time as Chief Whip between July 2016 and November 2017.

She told Channel 4 News he had used MPs’ mental and physical health problems as “leverage”, and called his conduct “threatening” and “intimidating”.

She added: “It’s an image he cultivates. I think he feels that he’s Francis Urquhart from House of Cards.”

The Prime Minister has been heavily criticised for bring his ally back into Government despite knowing about a complaint made by Ms Morton.

Labour Party chair Anneliese Dodds said Ms Morton’s decision to report Sir Gavin to the ICGS showed a “lack of faith in the Conservative Party complaints process”. She said: “The buck stops with Rishi Sunak. He was warned about Gavin Williamson’s behaviour and appointed him anyway.”

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

Cabinet Office spokeswoman Christine Jardine said: “Anything less would be an abdication of leadership from No 10, and make a mockery of Sunak’s promise to govern with integrity.

“The findings must be made public – if the Conservatives have nothing to hide, they have nothing to fear.”

Work and Pensions Secretary Mel Stride said it would be “utterly, utterly unacceptable” if Sir Gavin Williamson had told a senior civil servant to “slit your throat”, but also insisted the report was in the “realm of media speculation”.

Mr Stride said: “I think the important thing we do now is not to start intervening … and opining on who’s right and wrong or what may or may not have happened, but to wait for the results of that investigation.

“And then when we have that, and any other investigation that may be triggered in the meantime, then I think we can take stock and come to a firm conclusion.”

Any investigation could take several weeks, with Mr Stride suggesting Sir Gavin will still be in post by Christmas as any process “will take some time and we’ve got to wait to see what comes out of that”.

Shadow home secretary Yvette Cooper accused the prime minister of making “grubby political deals that aren’t in the national interest” to appoint Sir Gavin and Suella Braverman as Home Secretary.

The Cabinet Office said it had not received notice of any formal complaints about Sir Gavin’s behaviour.

Former Tory cabinet minister Baroness Morgan said she had “run-ins” with Sir Gavin when he was Theresa May’s chief whip, adding: “None of this surprises me, sadly.”