A senior civil servant claims Gavin Williamson told them to “slit your throat” in what they felt was a sustained campaign of bullying while he was defence secretary. The Ministry of Defence official told the Guardian Williamson made the extraordinary remarks in front of other civil servants in a meeting, and on a separate occasion told them to “jump out of the window”. The Whitehall aide, who worked closely with the cabinet minister, claimed Williamson “deliberately demeaned and intimidated” them on a regular basis. They reported the behaviour unofficially to the MoD’s head of human resources and took contemporaneous notes of the alleged incidents, but decided against making a formal complaint against the cabinet minister at that time. Williamson, who was defence secretary from November 2017 until May 2019 when he was sacked after a leak from the national security council, was said to have “shouted and raged”. The senior civil servant, who later left government, said the abuse was so bad that a senior military aide working in the department had later apologised for not calling it out. Williamson denied that he bullied the civil servant and said he had good working relationships with his officials. However, the Guardian understands that he is not denying that he used those specific words. In a statement, he 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.” The claims come after Downing Street said No 10 had “full confidence” in the Cabinet Office minister despite the emergence of bullying claims and abusive text messages he sent to the former Conservative chief whip Wendy Morton. Speaking at the Cop27 summit in Egypt, Rishi Sunak said: “There’s an independent complaints investigation that is happening and it’s right that we let that process run its course before passing judgment. I want to see the results of that, obviously, but I’ve been very clear that language is not right, it’s not acceptable. And that’s why I welcome the fact that Gavin Williamson has expressed regret about that and now we wait to see what the investigation says.” The latest allegation poses yet more questions for the prime minister about his political judgment after he decided to reappoint Williamson – a close political ally who is seen to have played a key role in his leadership campaign – to government despite being aware of Morton’s complaint. Text messages revealed over the weekend included angry remonstrations about not being invited to the Queen’s funeral and one that said “there is a price for everything”. The prime minister’s spokesperson said on Monday that Sunak had a zero-tolerance approach to bullying, but had refused to sack Williamson, claiming he had an “important contribution to make to government”. Meanwhile, the Times reported on Monday that an MP claimed Williamson, when he was chief whip in 2016, threatened her with potentially revealing details about her private life. The MP was now a minister, the paper said. She told the paper he called her to his office when she was campaigning on a politically sensitive issue and raised something about her private life “which she interpreted as a tacit threat”. Unnamed allies of Williamson said this had not been a threat and he had raised the issue in a “pastoral capacity”. Grant Shapps, the business secretary, said the messages should not have been sent, telling Sky News: “I don’t think it was the right thing to do, to send messages like that. I see they must have been sent in a moment of frustration. I think, generally, it is the case that it’s much better to write things which you would not live to regret later.” Williamson was sacked first as defence secretary by Theresa May after it was alleged he leaked details of a national security council meeting – an allegation he has always denied; and later as education secretary by Boris Johnson over the Covid 19 A-levels debacle. Labour and the Lib Dems have called on Sunak to sack Williamson. Anneliese Dodds, the Labour party chair, said on Monday night: “These allegations are extremely serious and speak to the toxic culture at the top of the Conservative party. The prime minister knew there was a complaint against Gavin Williamson but appointed him anyway. “He was given a seat around the cabinet table because Rishi Sunak was too weak to face a vote of his own party. Here again we see the grubby deal made by Rishi Sunak to put party management over the national interest.”