A former senior civil servant who claimed Sir Gavin Williamson told them to “slit your throat” has made a formal complaint against him, telling Sky News’ Beth Rigby his “words and actions had an extreme impact on my mental health”.

The allegations were made last night in The Guardian and included claims that Sir Gavin, who was the defence secretary at the time, told the official on another occasion to “jump out of the window“.

The Ministry of Defence official claimed his behaviour amounted to a sustained campaign of bullying.

The official, who later left government, said Sir Gavin “deliberately demeaned and intimidated” them on a regular basis.

They reported the incidents informally to the head of human resources, but decided against making a formal complaint at the time.

Sir Gavin, who ran the department between November 2017 until May 2019, said: “I strongly reject this allegation and have enjoyed good working relationships with the many brilliant officials I have worked with across government.

“No specific allegations have ever been brought to my attention.”

More on Gavin Williamson

Tonight the Cabinet Office minister faced fresh accusations from Anne Milton, the Tory former deputy chief whip, who told Channel 4 News that he “loved salacious gossip and would use it as leverage against MPs if the need arose” when running the whip’s office.

Ms Milton also claimed he used an MP’s financial situation as a source of leverage, telling the programme: “I do remember him asking me to give the MP in question the cheque.

“And he waved it under my nose and said, ‘Make sure when you give him this cheque, he knows I now own him’.”

She added: “I don’t think it was a joke. It was the seriousness with which he said it. And I think that the bottom line is, if instances accord with your overall experience with somebody, then you believe them.”

Sky News has approached Sir Gavin for a response to Ms Milton’s allegations.

Earlier, Downing Street described the allegations from the former civil servant as “serious” and said it would consider “proper processes” before commenting further.

The civil servant has now told our political editor Beth Rigby that they will formally complain to the Independent Complaints and Grievance Scheme (ICGS), parliament’s independent watchdog.

In a statement, they said: “This was an incredibly difficult period for me. Gavin Williamson’s words and actions had an extreme impact on my mental health.

“Government ministers have a code of conduct that they are required to follow. Any form of abuse is unacceptable.”

The former civil servant said they had decided to come forward “after feeling stronger given the passage of time”.

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Williamson and his spider had ‘mystique’ about them

The new complaint comes hours after it was confirmed former chief whip Wendy Morton had referred another allegation made against Sir Gavin – that he sent “abusive” messages to her – to the ICGS.

The Cabinet Office minister is already subject to an internal Conservative Party investigation over the series of threatening messages reportedly send to Ms Morton, complaining he had been excluded from the Queen’s funeral.

Sir Gavin served as Theresa May’s chief whip from 2016 and then as defence secretary from November 2017 until May 2019, but was fired over a row around a leak from government.

He was hired back by Boris Johnson as education secretary two months later, but was again ousted in September 2021 after much criticism of his handling of the brief during the pandemic.

Mr Sunak brought him back into government two weeks ago to serve as a Cabinet Office minister who also attends cabinet.