The Metropolitan police commissioner, Sir Ian Blair, yesterday attacked the decision to prosecute his force under health and safety laws for shooting dead an innocent man who was mistaken for a suicide bomber. Sir Ian, speaking for the first time about his force's pending prosecution over the death of Jean Charles de Menezes, said it could be "very significant" for everyday policing.

The Crown Prosecution Service ruled last week that no individual officer should face charges over the death, but that the Met should be charged under 1974 health and safety laws for breaching the duty of care it owed Mr de Menezes.

The Brazilian was shot dead last July by two police officers on a tube train at Stockwell underground station in south London, one day after failed suicide bomb attacks on the capital's transport system.

Mr Blair was speaking to the Metropolitan Police Authority (MPA), which itself yesterday decided to oppose the prosecution and urge the attorney general to halt it. Mr Blair said: "If this health and safety prosecution goes ahead it will be a fundamental turning point in policing.

"This goes right to the heart of the policing mission, mandate, the nature of risk-taking and the nature of assessing risks beforehand. I am not sure that was the design of the legislators in 1974 and it will be a matter that the courts will have to decide because the implications for everyday policing will be very significant."

The decision to prosecute the Met has led the Independent Police Complaints Commission to delay publishing its report into the force's mistakes. The MPA will write to the home secretary urging "a public mechanism" be found to examine the failings that cost Mr de Menezes his life.

Asad Rehman, of the Menezes family campaign, said: "We think the MPA should be writing to the attorney general that the inquest should take precedence over the health and safety prosecution." The first hearing is scheduled for August 14, with the trial not due until next year.

Yesterday Richard Barnes, a member and former deputy chair of the MPA, launched an outspoken attack on the force's handling of the de Menezes affair.

"Is there no one within [the Met] with the moral fibre and sense of personal obligation to recognise that Jean Charles's fate was sealed by systemic failure?" he asked. "The power to exercise ultimate force carries with it the responsibility to ensure all other possible alternatives are exhausted, even in such a fast-moving, fluid situation. Those obligations were not fulfilled at Stockwell, and Jean Charles paid the ultimate price for that failure."

He added: "I find it repugnant, and an affront to common decency, that the establishment can get it so wrong and then close ranks to protect its members from accepting and exercising the obligations of office. It is simply not enough to accept the glittering prizes, whilst ignoring the failures. Where is the man of personal stature and integrity amongst them?"

Mr Barnes, who is the Tory policing spokesman in London, said the shooting was followed by "various leaks that intended to besmirch his [Mr Menezes'] character. The source of this information is questionable, but it most probably came from those in authority. An innocent man was shot dead, and it was thought appropriate to traduce his character."