Ministers should behave “professionally and courteously” when dealing with their officials, the head of the civil service has said.
Sir Mark Sedwill told MPs that he could not comment on the allegations of bullying against Home Secretary Priti Patel, which she denies.
But he said there was an “expectation” that “professional people conduct professional relationships”.
He said ex-Home Office boss Sir Philip Rutnam’s resignation was “regrettable”.
Last month, Sir Philip quit his role saying there had been a “vicious and orchestrated” campaign against him in Ms Patel’s office.
The prime minister has given Ms Patel his support, but the Cabinet Office is investigating whether she broke the ministerial code.
BBC political editor Laura Kuenssberg said Sir Mark’s comments come at a time when relations between ministers and officials are tense.
Giving evidence to the Commons Public Administration and Constitutional Affairs Committee, Sir Mark refused to discuss specifics of the case and declined to discuss any advice given to the prime minister before Ms Patel’s appointment, saying his advice to the prime minister is “private”.
But he said: “Our expectation is that these are professional people – as in any big organisation.
“The job of the civil service is to support ministers, build a relationship of confidence and trust with them.
“The expectation on ministers also to conduct themselves professionally and courteously and try to get the best out of their civil service team.
“That is the most effective way of delivering the government’s agenda. If it doesn’t work, then it doesn’t work and we will take whatever the appropriate action might be.”
He said Sir Philip’s resignation was “very regrettable” and he had hope it could have been avoided.
But he would not comment further on the case, saying there was an ongoing investigation and potential legal action brought by Sir Philip.
The Cabinet Office is leading an internal inquiry to “establish the facts” regarding Sir Philip’s claims and whether they represented a breach of the ministerial code.
Sir Mark also warned against “over-defining” in the ministerial code what constitutes bullying and he said he has never sent a minister for behavioural coaching.