BORIS Johnson’s decision to stick with Priti Patel despite bullying accusations is to be the subject of a High Court legal challenge.

The FDA union launched judicial review proceedings in February over the Prime Minister’s move last year to disregard the findings of his adviser on ministerial standards in order to back the Home Secretary.

The case is due to be heard by Lord Justice Lewis and Justice Steyn at the Royal Courts of Justice in London on Wednesday.

In an investigation into Patel’s behaviour, published in November, Sir Alex Allan found she had not always treated civil servants with “consideration and respect”.

He concluded that Patel’s behaviour, which was said to include some occasions of shouting and swearing, met the definition of bullying adopted by the Civil Service.

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Allan left his advisory role in Downing Street after Johnson contradicted his advice by judging that Patel did not breach the ministerial code Ministers are usually expected to resign if they breach the code but Johnson, who is its arbiter, judged Patel had not fallen foul of the rules – and that is the decision being challenged by the FDA.

The FDA general secretary, Dave Penman, whose union represents senior public servants, said earlier this month that Johnson’s decision was “extraordinary” and that civil servants’ confidence in challenging unacceptable behaviour from ministers had been “fatally damaged”.

He said: “We are asking the court to rule that the Prime Minister misdirected himself. This is not about forcing the Home Secretary to face sanctions, that is a matter for the Prime Minister, this is simply about how the ministerial code is interpreted.”

Following the publication of Sir Alex’s report, Patel issued an “unreserved, fulsome apology” and said there were “no excuses” for what happened.

The hearing is due to start at 10.30am and expected to last two days.