Rishi Sunak has been urged to suspend Deputy Prime Minister Dominic Raab while an investigation into bullying allegations is carried out.
The three permanent secretaries who led officials working under Mr Raab are thought to have given evidence to an inquiry into the Justice Secretary being led by senior lawyer Adam Tolley KC.
Dozens of civil servants are believed to be involved in eight formal complaints.
Dave Penman, leader of the FDA union, which represents senior officials, said Mr Raab should be suspended to protect other members of staff while the investigation is conducted.
“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.
“That’s not to prejudge the investigation, that’s to say if there are serious allegations of bullying and extensive allegations like this, that one of the considerations is how do you protect employees from that sort of behaviour? And while it’s being determined, you would normally suspend someone, given the seriousness and extent of those accusations.”
Former Foreign Office mandarin Lord Simon McDonald has reportedly given evidence to Mr Tolley as a witness, while Antonia Romeo, the current permanent secretary at the Ministry of Justice, and Philip Rycroft, who ran the Brexit department while Mr Raab was there, are also thought to have been spoken to.
Mr Rycroft appeared to confirm he had been interviewed, saying “it would be a bit of a surprise if the investigation hadn’t reached out to those who were working with Dominic Raab through those years”.
He also told Times Radio on Wednesday: “I’m pleased the investigation is happening. 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.”
Mr Penman said: “The person who works closest with a government minister is the permanent secretary and so you would have expected that, if concerns have been raised about his behaviour, then those concerns would have been raised with the permanent secretaries of the time, who may well have spoken to Dominic Raab.”
The Education Secretary told Sky News: “I personally think it is fair to let investigations continue.
“I think that is the fair process. I think it was Dom himself who instigated this investigation. That is ongoing. That will uncover all the facts. When you get the facts you discuss and take the action.
“I think it is only fair when somebody accuses somebody of something you go through that. You go through the fair process. I think that is the right thing to do.
“Then the Prime Minister and Dominic will obviously discuss that and make the right decision based on that.”
Ms Keegan said she does not feel uncomfortable sitting alongside someone accused of bullying.
“I sit round the Cabinet table and don’t see that. I feel very comfortable with my colleagues around the Cabinet,” she said.
The Liberal Democrats called on the Prime Minister to publish the advice given to him by the Cabinet Office when he appointed Mr Raab in October.
Downing Street has stressed Mr Sunak was not aware of any formal complaints against Mr Raab when he appointed him Deputy Prime Minister, but has refused to comment on what information he had been given.
Deputy Lib Dem leader Daisy Cooper said: “It’s time for the Prime Minister to come out of hiding and face the music.
“The public deserves to know the truth about what he knew and when, including the full disclosure of any advice given to him by the Cabinet Office.
“Raab is just the latest of Sunak’s appointees who has been caught up in scandal.
“If Rishi Sunak was serious about integrity, he would give the Tolley inquiry the full co-operation it deserves by providing his own formal evidence.”