The failed raid is the latest in a string of controversies engulfing Sir Ian as he fights for his job as commissioner of London's Metropolitan Police Service, known as the Met.

Prime Minister Tony Blair and London Mayor Ken Livingstone have been forced to back him amid calls for his resignation, most notably one from a member of the Metropolitan Police Authority, which oversees the Met.

Since taking the post in February 2005, Sir Ian has presided over the fatal shooting of Jean Charles de Menezes, a Brazilian electrician police thought was a suicide bomber. Many analysts believe the old-guard members in the force are also waging a campaign to discredit the reform-minded Sir Ian.

Now his future hangs on the outcome of an inquiry into the de Menezes shooting.

'He's going to be under pressure for some time,' said Tim Newburn, professor of criminology at the London School of Economics. 'It shows no sign of going away. There are various people who quite clearly have an agenda, which includes seeing if they can remove the commissioner from his job. A lot will depend on what is said in the IPCC [Independent Police Complaints Commission] report.'

Police shot and killed de Menezes, 27, on the London subway system, known as the Tube, on July 22, two weeks after four suicide bombers blew themselves up in attacks that rocked the British capital. Police were under tremendous pressure to stop other attacks and flawed intelligence led them to put de Menezes under surveillance. Officers followed him and, believing he was another suicide bomber, shot him eight times after he got onto a subway train that morning.

After the shooting, the commission launched an inquiry, which it said would be published as soon as possible. But the inquiry report was leaked last weekend and local newspapers said it details a list of blunders and mistakes that could spell the end for Sir Ian, 53.

The leaks appear to be part of a campaign of attacks against Sir Ian by his own colleagues. The commissioner, who studied English at Oxford University, joined the force right after graduation. He rose quickly through the ranks, making a name for himself as a thoughtful, intelligent, progressive officer. After taking control of the force, one of the largest in the world with 31,000 officers, he said he wanted to inject more ethnic diversity into the force and championed radical ideas such as community support officers.

His unconventional background put him at odds with the traditionalist officers in the force, said Professor Newburn. 'Ian Blair went into the job as a reformist police officer wanting to make all kinds of changes. It's not surprising there are officers who feel sufficiently uncomfortable and want to see him depart his post.'

Chris Williams of the Open University's European Centre for the Study of Policing said battling leaks came with the job. 'The senior ranks of the Met police have always been full of highly ambitious people, all leaking against each other.'

But Sir Ian's attempt to stall the investigation could be a bigger problem for him, said Dr Williams.

'It's not the cock-up, it's the cover-up,' he said. 'The big blunder that falls to him and him alone is his reaction to the de Menezes shooting when he tried to avoid the inquiry by the IPCC, which is a statutory requirement.'

Sir Ian told the commission and the Home Office that commission investigators would not be given immediate access to vital evidence. As a result, doubts have been raised over surveillance camera footage and there are reports log books were doctored. 'This undermines the credibility of what the IPCC can find. Even if the IPCC can produce an account of events, we're less certain of the accuracy of events,' Dr Williams said.

Since last summer, Sir Ian has been involved in other controversies. In January, he slammed the media for being racist, saying the press reported on crimes involving whites more often than minorities and wondered why so much attention was paid to the murders of two 14-year old white girls. In March, it was revealed he had secretly taped some phone calls with the attorney-general, Lord Goldsmith.

Then came the Forest Gate raid, in which the brothers were arrested on a tip from an informant. A pyjama-clad Mr Kahar, who works at both the post office and a supermarket, was shot in the shoulder.

The actions have aggravated relations between the police and London's sizeable Muslim community. Fahad Ansari, spokesman for the Islamic Human Rights Commission, said his group has been calling for Sir Ian to step down since the de Menezes shooting.

'He's not competent - either it's deliberate or incompetent,' Mr Ansari said, adding the police should be more cautious when dealing with the Muslim community.

'We've had these raids before; we've had these faulty intelligence situations, where the whole community is demonised because of a tip-off from someone who has a grudge. There are elements of society who want to destroy Britain from within. It's a whole climate of fear based on suspicion.'