Sir Gavin Williamson has denied new allegations of bullying after an official made a claim.
When Sir Gavin was defence secretary, he allegedly told a senior civil servant to “slit your throat” and “jump out the window.”
Sir Gavin is also being investigated by Parliament’s bullying watchdog for sending expletive-laden messages to former chief whip Wendy Morton.
He has “strongly” rejected allegations of bullying.
An unnamed official told the Guardian Sir Gavin, who is now a Cabinet Office minister in Rishi Sunak’s government, “deliberately demeaned and intimidated” them.
The official said they raised concerns to the Ministry of Defence’s human resources department but made no formal complaint.
In a statement, 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.
“No specific allegations have ever been brought to my attention.”
Mr Williamson does not deny using the language.
A government spokesperson said the Cabinet Office, where Mr Williamson now serves as a minister, had “not received notice of any formal complaints about Gavin Williamson’s behaviour from his time at the Ministry of Defence or any other department.”
Labour’s party chair Anneliese Dodds said the allegations were “extremely serious” adding they “speak to the toxic culture at the top of the Conservative Party”.
Sir Gavin reportedly sent a series of abusive WhatsApp messages to Ms Morton accusing the government of excluding certain MPs from the Queen’s funeral service at Westminster Abbey.
Last month, Ms Morton sent the messages to the Conservative Party after making a formal complaint about Sir Gavin’s behaviour.
On Tuesday, she referred Sir Gavin to Parliament’s Independent Complaints and Grievance Scheme. The independent body looks into claims of parliamentarians and staff who feel they have been bullied or harassed.
Gavin Williamson is not a universally popular figure. That’s being polite. Some of his colleagues don’t have much time for him at all.
But he has been a key ally of Rishi Sunak in recent months as the prime minister fought his way into Downing Street.
He was rewarded with a ministerial job and a seat around the cabinet table. It’s not completely clear yet what that job involves, but he’s based in the Cabinet Office with another key Sunak ally, Oliver Dowden.
Mr Sunak appears to be trying to ride this one out at the moment, waiting to see what happens with a complaint made by Wendy Morton.
But Sir Gavin has many critics who dislike his style and think his influence is exaggerated.
Prime Minister Rishi Sunak has said the language Sir Gavin used was “not acceptable”, but No 10 insisted he still has confidence in him.
In the messages to Ms Morton, published by the Sunday Times, Sir Gavin is said to have warned the former chief whip “not to push him about” and that “there is a price for everything”.
Sir Gavin told the paper: “I of course regret getting frustrated about the way colleagues and I felt we were being treated.”
Asked if it amounted to bullying, Mr Sunak said “an independent complaints process” was under way and it would be “right to let that process conclude”.
The former architectural design firm director, 46, had served as defence secretary under Theresa May and education secretary under Boris Johnson, and was sacked from both roles.
Mr Sunak, who replaced Liz Truss as prime minister last month, brought Sir Gavin back into government as Minister without Portfolio.
Sir Gavin’s current governmental responsibilities are not clear.
Work and Pensions Secretary Mel Stride said Sir Gavin’s role in government was “very important”.
Mr Stride told Times Radio: “I think Gavin is somebody who, as I say, has particular talents and a particular understanding of the parliamentary party.”
The deputy leader of the Liberal Democrats, Daisy Cooper, has said his return raised “yet more serious questions about Rishi Sunak’s judgement”.
“If the prime minister was serious about restoring integrity he would sack Gavin Williamson,” she said.