BORIS Johnson has written to all UK ministers and heads of government departments reminding them that there is “no place for bullying” after the Whitehall probe into the Home Secretary found she had shouted and sworn at staff.

Last week, Sir Alex Allan, the Prime Minister’s adviser on ministerial standards, resigned after Mr Johnson overruled his conclusion that Priti Patel had bullied staff, albeit unintentionally, and so had breached the ministerial code. The PM, who is the final arbiter of what constitutes a breach, decided his Cabinet colleague had not broken the rules and made clear he had full confidence in her.

Only the week before, Mr Johnson had seen two of his most senior advisers, Dominic Cummings, his de facto Chief of Staff, and Lee Cain, his Director of Communications, announce their departure from No 10.

Over the weekend, Downing Street did not deny suggestions that the PM had tried and failed to convince Sir Alex to tone down his conclusion – published during anti-bullying week – that Ms Patel’s behaviour amounted to bullying.

Issuing a written ministerial statement, Mr Johnson acknowledged that Sir Alex had concluded that Ms Patel’s behaviour could “on occasion” be described “as bullying in terms of the impact felt by individuals” but made clear he was standing by the Home Secretary and considered “this matter now closed”.

The PM, referring to a joint letter with Simon Case, the Cabinet Secretary, to all ministers and permanent secretaries, said: “It sets out the paramount importance of relationships of mutual trust and respect between politicians and their officials.

“This includes keeping internal conversations private, feeling able to speak freely and honestly about matters of state and to speak constructively about things that are not working so that we can fix them together promptly.

“I am clear that there is a particular duty on ministers and permanent secretaries to create jointly across Government a culture which is professional, respectful, focused and ambitious for change and in which there is no place for bullying.

“The Cabinet Secretary and I are enormously grateful to civil servants for the commitment they have shown as we navigate through these challenging times.”

Later, asked why the PM had sent out the letter, his spokesman said Mr Johnson was reaffirming his belief that a strong working relationship between ministers and their officials should be “at the heart of government”.

However, Dave Penman, who leads the FDA union of senior civil servants, noting how the PM set out in the foreword to the ministerial code, that there should be no bullying or harassment, said: “In the first test of his commitment to these words, he has transparently chosen partisan political interest over the interests of the victims of the Home Secretary’s behaviour as well as the broader standards that should rightly be expected of ministers.

“If the Prime Minister was serious about his commitment to these standards, he would introduce an independent and transparent process for dealing with these complaints, that was free from the political interference he has so blatantly shown in regard to the Home Secretary.”

Following the publication of Sir Alex’s report, the Home Secretary, who had denied any wrongdoing, apologised and said there were “no excuses” for what had happened.

Ms Patel said that “any upset that I’ve caused is completely unintentional and at the time, of course it says it’s in the report, that issues were not pointed out to me”.

Labour has called for the report into Ms Patel’s behaviour to be published in full.

Meanwhile, Lord Evans of Weardale, who chairs the standards watchdog, the Committee on Standards in Public Life, is due tomorrow to give evidence to the Commons Standards Committee as part of its inquiry into the code of conduct for MPs.

Lord Evans said that following Sir Alex’s report that this would be considered as the standards watchdog conducts its own inquiry into the ministerial code.