MPs have launched a scathing attack on the police watchdog, accusing it of being "woefully under-equipped and hamstrung."
The home affairs select committee said the Independent Police Complaints Commission (IPCC) should be given a statutory power to require a force to implement its findings.
The committee also said that more cases should be investigated by the IPCC instead of being referred back to the original police force on a "complaints roundabout."
There have long been concerns that the IPCC lacks the requisite impartiality and campaigners have claimed it is too close to the forces it is charged with investigating.
Campaign group Inquest welcomed the committee's findings. Co-director Deborah Coles said: "The importance of robust oversight of policing cannot be underestimated. It is alarming how many people die in police custody in tragically similar circumstances.
"Until we have robust independent investigations that are capable of holding police to account and ensuring learning is implemented people will continue to die."
Committee chairman Keith Vaz MP 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."