The Government was under pressure to provide further funds to the police watchdog today after a damning report found it lacks the resources needed to get to the truth.
The Independent Police Complaints Commission (IPCC), which is investigating the Hillsborough disaster in the UK's biggest ever inquiry into police misconduct, is "woefully under-equipped and hamstrung", an influential group of MPs found.
The report from the Home Affairs Select Committee said around 200 police officers retire or resign each year to avoid disciplinary hearings.
IPCC chairwoman Dame Anne Owers said without further resources the body will struggle to meet the expectations of complainants and bereaved families.
The Home Office said it is already working to ensure the IPCC has the powers and resources it needs and is to shortly reveal new measures to improve trust in the police.
Committee chairman Keith Vaz said: "When public trust in the police is tested by complaints of negligence, misconduct and corruption, a strong watchdog is vital to get to the truth - but the IPCC leaves the public frustrated and faithless."
He added: "Nearly a quarter of officers were subject to a complaint last year. Many were trivial, but some were extremely serious, involving deaths in custody or corruption. It is an insult to all concerned to do no more than scratch the surface of these alleged abuses.
"The IPCC investigated just a handful 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."
A total of 31,771 officers - one in four - were subject to a complaint during 2011/12 and when appeals were made against the way forces handled a complaint, the IPCC found that the police were wrong in one in three cases.
The watchdog should have a statutory power to force implementation of its recommendations and in the most serious cases it should instigate a "year on review" to ensure that its recommendations are properly carried out, the committee said.
Chief constables should be held to account if a force fails to implement the IPCC's recommendations following an investigation by Her Majesty's Inspectorate of Constabulary and the local police and crime commissioner.
More cases should be investigated independently by the IPCC instead of being referred back to the original police force on a "complaints roundabout", the report added.
It also said the IPCC - which has made 63 staff redundant in the past two years - has a smaller budget than the Professional Standards Department of the Metropolitan Police alone.
A backlog of appeals is building up at the commission since the need to make financial savings forced it to reduce its temporary staff.
The Government should maintain funding for anti-corruption cases at the same level committed to investigate the Hillsborough disaster, the committee said.
Dame Anne said: "This report recognises that we do not yet have the resources or powers to do all that the public rightly expects and needs from us. That is what we have been saying for a long time.
"Without that, we will continue to struggle to meet the legitimate expectations of complainants and of families who have lost someone in tragic circumstances."
Dame Anne said the commission was in the middle of a recruitment campaign to attract a a more diverse range of investigators but existing staff were under increasing pressure.
She went on: "But all of this needs resources and powers. That is what we have been promised for the Hillsborough investigation, which will allow us to show what we can do and how we can do it. We want that to be a model of how we go forward."
The report said cases involving serious corruption, such as tampering with evidence, should be automatically referred to the IPCC for independent investigation.
It added that the IPCC should be investigating the "plebgate" allegations surrounding former Tory chief whip Andrew Mitchell's row with police officers in Downing Street last year.
When Metropolitan Police Commissioner Sir Bernard Hogan-Howe was asked why the investigation was not passed on to the commission, he told the committee that "we did try, we did ask them, of course. They concluded they either could not or would not".
Shadow home secretary Yvette Cooper said: "The Home Affairs Select Committee is right that the IPCC is not strong enough to tackle the problem when policing goes wrong."
She added: "For the public to have confidence in the high standards of British policing, they also need to know that there will be swift, robust action when policing goes wrong."
The watchdog, which was established in 2004, investigates the most serious complaints against the police, as well as the Serious Organised Crime Agency, Her Majesty's Revenue and Customs and the UK Border Agency.
A Home Office spokesman said: "Improving police professionalism and integrity are at the cornerstone of the sweeping reforms we are making to the police force, and the IPCC has a key role to play.
"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."
In addition the committee said private firms - like G4S, Capita, Mitie and Serco - involved in delivering services that would once have fallen solely to the police should fall under the watch of the IPCC.
John Shaw, G4S managing director of policing support services, supported the call.