Health Secretary Matt Hancock has defended Priti Patel as "courteous" following bullying claims made by the ex-top civil servant in her department.
Sir Philip Rutnam, the Home Office's most senior official, resigned on Saturday citing a "vicious and orchestrated" campaign against him.
The BBC has also learnt that a formal complaint about Ms Patel's conduct was made when she was employment minister.
The home secretary has previously denied she mistreated staff.
Responding to Sir Philip's departure, shadow chancellor John McDonnell told Sky News the situation was "unprecedented" and suggested that Ms Patel was "on the way out".
