Sir Gavin Williamson allegedly told a senior civil servant to "slit your throat" in what they claimed was a bullying campaign while he was Defence Secretary.
Rishi Sunak is under increasing pressure over his decision to bring his ally back into Government after reports of fresh incendiary claims about his conduct.
The Ministry of Defence (MoD) official said Sir Gavin made the remarks in front of colleagues in a meeting, and on another occasion told them to "jump out of the window".
