The Independent Police Complaints Commission is under-funded and cannot cope with the demands of scrutinising the 43 separate forces in England and Wales, according to the home affairs committee.
In a report about the effectiveness of the police watchdog, the Commons committee says “the public do not fully trust the IPCC” and that nearly a quarter of officers – 31,771 – were subject to a complaint last year.
Although many of these complaints were trivial, some involved deaths in custody or corruption, but committee chairman Keith Vaz said the IPCC had only managed to “scratch the surface of these alleged abuses”.
The report found that the IPCC was over-loaded with appeal cases, serious cases involving corruption or misconduct were under-investigated and public trust was undermined by the organisation’s dependence on the police to carry out inquiries.
At the same time, the commission was under-resourced and could not afford to do any more.
Mr Vaz said the IPCC was “woefully under-equipped” and “leaves the public frustrated and faithless”.
He added: “The IPCC investigated just a handful (of complaints) and often arrived at the scene late, when the trail had gone cold. The commission is on the brink of letting grave misconduct go uninvestigated.
Andrew Mitchell investigation
The home affairs committee says it is "concerned" that the IPCC did not opt to carry out an independent investigation into the Andrew Mitchell affair, but decided to leave this to the Metropolitan police.
It says: "The allegation that a serving (Met) police officer may have fabricated an account and concealed that he was an officer is an extremely serious matter and raises broad questions about the integrity and honesty of some officers.
"Allegations following the altercation between Rt Hon Andrew Mitchell MP and police officers raise fundamental questions about police honesty and integrity."
In December, Channel 4 News and Dispatches revealed that CCTV footage of this altercation in Downing Street in September - during which Mr Mitchell was alleged to have called a police officer a "pleb" - cast doubt on the account in police logs leaked to the media.
The furore had led to Mr Mitchell's resignation as chief whip in October.
“It is buried under the weight of poor police investigations and bound by its limited powers. The public are bewildered by its continued reliance on the very forces it is investigating.
“The complaints and appeals process is frustrating, time-consuming and frequently flawed.”
The committee says the IPCC “has neither the powers nor the resources that it needs to get to the truth when the integrity of the police is in doubt”.
It “lacks the investigative resources necessary to get to the truth, police forces are too often left to investigate themselves, and the voice of the IPCC does not have binding authority”.
The committee believes more complaints should be investigated directly by the IPCC, with the commission taking immediate control of a potential crime scene at the beginning of inquiries into serious allegations.
It also says the IPCC should be given a statutory power to require a force to implement its findings, with officers routinely interviewed under caution in the most serious cases.
The remit of the commission should be extended to cover private sector contractors, it says, and the IPCC should be renamed, possibly as the Independent Policing Standards Authority.
A Home Office spokesman said: “We are already working to ensure the organisation has the powers and resources it needs to manage the challenges it is currently facing and we will shortly announce a package of new measures designed to further improve the public’s trust in the police.”