LONDON, Oct 2, 2008 (AFP) - Britain's top policeman, Metropolitan Police chief Ian Blair, announced his resignation Thursday after months of pressure, notably over the fatal shooting of an innocent suspect and racism allegations.

Blair, who came to office shortly before suicide bombings in London in July 2005, said he had lost the backing of new London mayor Boris Johnson, who took office in May.

'I have today offered my resignation as commissioner to the Home Secretary, .. she has reluctantly but graciously accepted,' he told a hastily arranged press conference, adding that he would stand down on December 1.

'Without the mayor's backing I do not consider that I can continue in the job,' he added.

Blair has long faced criticism over the death of Jean Charles de Menezes, an innocent Brazilian shot dead by police who mistook him for a suicide bomber in the wake of July 2005 bombings in London, which killed 56.

Then in August the Met's top Muslim officer, Assistant Commissioner Tarique Ghaffur, confirmed that he was taking Blair to an employment tribunal over alleged racism.

And a new media report Thursday claimed that Blair had used public money to pay a close friend more than 15,000 pounds (26,400 dollars, 19,000 euros) to help him sharpen up his image when he became Met chief in 2005.

The Daily Mail reported that the friend, who had known Blair for 30 years, was the owner of a company that won a contract to help him 'make the transition.' The friend had received more than three million pounds' worth of police contract work.

The Guardian newspaper said on its online version that it had been the Daily Mail report that had apparently prompted Blair's expected resignation.

The De Menezes killing has been the main cloud hanging over him. Scotland Yard was heavily criticised in a report in August 2007 on the killing, although Blair himself escaped censure.

The pressure mounted on him last November 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.'

An inquest into the killing is currently underway in London.

Some commentators feel that Blair's position was made less secure by the election of conservative Johnson as London mayor.

Former mayor Ken Livingstone had staunchly defended Blair through repeated storms, but Johnson was clearly cooler, and had not publicly backed the Met chief.

Among the favourites to succeed him is Hugh Orde, the chief constable of the Police Service of Northern Ireland; Blair's deputy Paul Stephenson, 54; and Ronnie Flanagan, the Chief Inspector of Constabulary.

Speaking before Blair's resignation was confirmed, Orde said: 'I have two years of my contract left here, I have no plans to move at the moment.'