Sir Gavin Williamson resigned from the UK government on Tuesday evening following a slew of bullying allegations and several formal investigations into his behaviour.
Williamson is alleged to have told a senior civil servant to “slit your throat” and another official to “jump out of the window” while serving as defence secretary.
In his letter to prime minister Rishi Sunak, the minister without portfolio said the allegations and investigation into his conduct “are becoming a distraction for the good work this government is doing for the British people.”
He added: “As you know, there is an ongoing complaints process concerning text messages I sent to a colleague. I am complying with this process and have apologised to the recipient for those messages.”
Williamson added he was resigning “with real sadness” and would continue to support the Sunak government as a backbench MP.
Until his resignation, Williamson was facing an informal investigation by Downing Street into his behaviour. He is also facing an inquiry by parliament’s Independent Complaints and Grievance Scheme.
Former chief whip Wendy Morton on Tuesday made a formal complaint about Williamson’s behaviour to the ICGS, which oversees MPs’ conduct.
The move follows claims by her of bullying by Williamson after he sent her expletive-laden texts about the allocation of places at Queen Elizabeth’s funeral.
Williamson, who last month returned to government as a fixer for Sunak based in the Cabinet Office, on Tuesday did not deny using specific words, but did deny allegations of bullying, saying that he had had “good working relationships” with civil servants in the departments he had worked in.
Number 10 previously described the allegations against Williamson as “serious”.
Mel Stride, work and pensions secretary and a close ally of Sunak, said Williamson’s alleged comments were “utterly unacceptable”.
Asked by Sky News if Williamson was “unsackable”, Stride said: “I don’t think anybody is unsackable; I’m not unsackable.” He also confirmed that Williamson was under investigation by the ICGS following Morton’s complaint.
In a letter in response to Williamson’s quitting, Sunak said he supported his minister’s decision and understood why it had been taken.
“I know your commitment to successive Conservative governments and the party over the years has been unwavering,” he wrote. “I would like to thank you for your personal support and loyalty”.
Opposition parties roundly criticised Sunak’s leadership over the matter. Deputy Labour leader Angela Rayner argued that Williamson’s appointment was “a damning reflection of a weak prime minister”.
“Rishi Sunak appointed Gavin Williamson with full knowledge of serious allegations about his conduct and repeatedly expressed confidence in him,” she said. “This is yet another example of Rishi Sunak’s poor judgment and weak leadership.”
Liberal Democrat deputy leader Daisy Cooper argued that there needed to be clarification on “what Rishi Sunak knew about these shocking allegations and when”. She added: “[Sunak’s] promise to lead a government of integrity has now been left in tatters.”
Dave Penman, head of the FDA union, which represents senior civil servants, speaking before Williamson’s resignation, described the process for investigating the civil servants’ allegations as a “sham” and called on Sunak to appoint a new independent adviser on ministerial interests.
“Even if a civil servant came forward now with a fresh allegation about any minister, there is no way for that to be investigated. The entire process is a sham,” said Penman.
Lord Christopher Geidt, the last ethics adviser, resigned in June after a dispute with Boris Johnson over the ministerial code. Downing Street said Sunak intended to appoint a new adviser in due course.