The Metropolitan Police Federation has accused a police watchdog of bias.
The federation has more than 30,000 members
It has criticised the Independent Police Complaints Commission (IPCC) over a "catalogue of inappropriate comments and perverse actions".
The federation, which represents more than 30,000 London police officers, said the IPCC is behaving like a "pressure group with an agenda"
But IPCC chair Nick Hardwick said the federation had "misrepresented the views" of the organisation.
In a 12-page statement about the IPCC, which investigates police misconduct claims, the federation said it was becoming "increasingly disturbed" by the commission's actions.
Its main complaint is with the IPCC's handling of the inquiry into the shooting of Jean Charles de Menezes after he was mistaken for a suicide bomber at Stockwell last July and it feels "badly let down".
The federation has blamed the commission for a "spectacular" leak about the investigation and mismanaging the media strategy.
It has described a "disgraceful" press conference which, it claims, gave the impression the officers involved should probably face murder charges.
Mr Hardwick accepted there were instances where the IPCC had "got it wrong" as in the Stockwell Inquiry leak.
"Where this is the case we apologise and do our best to put it right," he said.
The IPCC was set up in 2004 to replace the Police Complaints Authority, which had been criticised for allowing police to check allegations about one another.
The IPCC has 84 investigators to look into claims of police misconduct and deaths in custody and stresses it is independent from police authorities.
But it has come under scrutiny, particularly following the leak to ITV News of papers relating to the investigation into Mr Menezes' death.