Dominic Raab’s accusers fear he will seek to cover up the bullying claims made against him by resigning before an investigation has concluded.
A Whitehall sleaze probe is currently looking into allegations made by dozens of civil servants about the Deputy PM’s behaviour.
But witnesses are concerned he will attempt to get it dropped by quitting when he is presented with the evidence against him.
Rishi Sunak has refused to give up a veto he holds over investigations into his ministers.
The terms of reference for the probe into Mr Raab state that they “may be updated at the discretion of the Prime Minister”.
Civil servants who have made complaints against him say they have been “through absolute hell” and must have their allegations made public.
They insist the investigation must be completed and its findings published no matter what the minister decides to do.
“They have put their heads above the parapet and made complaints against the Deputy Prime Minister,” a source said. “If they went through that and there was not a conclusion, it would be outrageous.”
A spokesman for Mr Raab said: "Dominic called for the investigation so he can answer any accusations put to him in a fair and formal setting and he fully intends to see it through."
The PM today did not dispute claims that he had been warned about Mr Raab’s behaviour before he gave him the job as his deputy.
Asked if he knew about concerns, Mr Sunak’s press secretary would only say: "The PM was not aware of any formal complaints at the time of appointing Dominic Raab."
At Prime Minister’s Questions, Labour leader Keir Starmer accused Mr Sunak of being "too weak" to act as he accused the Conservatives of having an "addiction to sleaze and scandal".
"How would he feel if one of his friends or relatives was being forced to work for a bully simply because the man at the top was too weak to do anything about it?" he asked Mr Sunak.
The PM said: "When I was made aware of formal complaints I appointed a leading independent KC to conduct an investigation, because I take action when these things happen."
Mr Raab, who was sitting next to the PM in the Commons, shook his head and muttered as the Labour leader questioned his appointment.
The Mirror revealed yesterday that officials involved in the complaints against Mr Raab have said they lost weight, suffered breakdowns or even felt suicidal as they thought there was no escape.
The three permanent secretaries who led officials working under Mr Raab are thought to have given evidence to the inquiry into Mr Raab being led by senior lawyer Adam Tolley KC.
The investigation centres on when he was foreign secretary, Brexit secretary and during his first stint as justice secretary. There are eight formal complaints involving at least 24 civil servants.
Phillip Rycroft, former permanent secretary at the Department for Exiting the EU, told Times Radio: "Clearly for everybody involved in this, getting this sorted out is long overdue, but we'll have to wait and see what the investigator comes up with, and, ultimately, the decision on the base of that evidence is one for the Prime Minister."
Dave Penman, leader of the FDA union, which represents senior officials, has called for Mr Raab to be suspended to protect other members of staff while the investigation is conducted.
"Dominic Raab is now facing investigations around eight separate complaints involving what we understand is dozens of civil servants in three separate government departments over a period of four years," he told BBC Radio 4's Today.
"If that was any other employee, if that was a permanent secretary in the civil service, they would in all likelihood be suspended from their job while the investigation took place."
Mr Raab was sacked as justice secretary and deputy prime minister by Liz Truss when she became PM in September. But the Esher and Walton MP was reappointed to both roles by Mr Sunak on his arrival in No10.
The Mirror revealed in November Mr Raab has been nicknamed “The Incinerator” because he “burns through” staff so quickly.
