Black police leaders are threatening to take legal action after the controversial Iranian-born officer Ali Dizaei was turned down for promotion yesterday.

Chief Superintendent Dizaei applied to become a commander, the fifth-highest rank at Scotland Yard. But a promotions board of the Metropolitan Police Authority (MPA) advised by Sir Ian Blair, the commissioner, selected three other candidates for vacant posts.

Mr Dizaei said that he would wait for feedback on his performance, but supporters accused the selectors of being biased. The MPA rejected the claim, and said that the authority had “appointed the people we judged to be up to the challenge. We did not appoint those whom we judged were not, or were not yet ready.”

Last week The Times published excerpts from Mr Dizaei’s autobiography, Not One of Us, in which he attacked the police’s handling of a four-year corruption investigation, and criticised individual officers. He said that a group of officers wanted to destroy his reputation and career. He was cleared by the Old Bailey in 2003 of perverting the course of justice and misconduct in public office.

Mr Dizaei, who is in charge of policing in the West London borough of Hounslow, said that he was disappointed by the result of his application, and would review his position after examining the feedback.

Mr Dizaei is a senior member of the National Black Police Association. Keith Jarrett, president of the association, said yesterday that he would be seeking an urgent meeting with Sir Ian. He said that he wanted to know why Mr Dizaei had been denied promotion when he led one of the best-performing boroughs in London, and had been graded as “exceptional” in his personal assessment. If the commissioner’s answers were not satisfactory, Mr Jarrett said, the association would take the matter further, possibly to an employment tribunal.

Mr Jarrett said that in the past five years there had been no promotions of senior black or Asian officers in the force. “I do not want to start levelling accusations of racism, but it worries me it could be a personal vendetta against Ali.”

The Metropolitan Police Black Police Association said: “We suspect the decision of the MPA was not free from bias and could not have been reached on the basis of objective and fair criteria.”

Len Duvall, chairman of the police authority, denied the “unwarranted attack”, saying that its appointments “were based, rationally and fairly, on merit” and that the three appointed officers were the best qualified for promotion at this time.

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