LONDON, Oct 2, 2008 (AFP) - Britain's top cop Sir Ian Blair, who resigned Thursday, was a career police officer whose tenure as head of London's Metropolitan Police was never lacking in controversy.

By the time he had risen to the top of the nation's police force in February 2005, just months before the suicide bombings on London's public transport network that left 56 dead, Blair had been a police officer for 31 years.

In the years since his promotion, however, he has been plagued by accusations of incompetence: first over the shooting of Brazilian electrician Jean Charles de Menezes; and then over allegations of racism made by Britain's top Muslim police officer.

Since joining the force in 1974 as a graduate trainee fresh out of Oxford University, Blair investigated crimes ranging from corruption to murder. He also published a book on rape investigations.

Born on March 19, 1953, Blair was educated in Shropshire, western England, and Los Angeles, before studying English Language and Literature at Oxford, where he gained a second class honours degree.

After serving as the ranks of constable, sergeant and then inspector in central London, Blair was promoted to Detective Chief Inspector in 1985, the same year he published 'Investigating Rape: A New Approach for Police'.

In 1993, he led one of the biggest corruption inquiries in London for more than a decade.

He became one of the Metropolitan Police's deputy commissioners in 2000 and three years later was awarded a knighthood by the Queen for his services to policing.

But having reached the top job in policing in 2005, he quickly found himself in the headlines for the wrong reasons.

Arguably the most serious crisis was the inquiry into de Menezes's death. The 27-year-old electrician was shot dead after having been mistaken for an on-the-run terrorist in the aftermath of the July 2005 bombings in London.

Although Scotland Yard was heavily criticised in a report in August 2007 on the mistaken killing, Blair himself escaped censure.

The pressure mounted on him in November 2007 after his police force was found guilty of breaching health and safety laws in the shooting.

But he fought off calls for his resignation, saying officers had done their best in a 'simply extraordinary situation.'

Then Blair came in for criticism after Britain's top Muslim policeman, Metropolitan Police Assistant Commissioner Tarique Ghaffur, accused him of racial discrimination.

Ghaffur confirmed in August that he was taking Blair to an employment tribunal, while denying the move was linked to unhappiness at not being promoted.

Ghaffur was suspended, and Britain's second most senior Muslim cop Commander Ali Dizaei met with the same fate after reportedly having advised defence lawyers on how to undermine a prosecution involving the Metropolitan Police.

Dizaei, president of the National Black Police Association, was cleared of corruption allegations in 2003 that had seen him suspended from work for two years.

Police in London have had to work hard to try and win the trust of British Muslims, particularly in the wake of the 2005 bombings, which was the first major challenge for Blair.