The Police Complaints Authority (PCA) also suggests that a record number of people are dying in custody, partly because the police are failing to learn lessons from previous fatalities. It says that failure to act on previous errors could lead to police chiefs, including chief constables. being prosecuted under the Human Rights Act, which comes into force in 2000.
The authority calls for urgent action to reduce the number of people dying in police custody, which totalled 53 last year at an estimated cost to the taxpayer of pounds 2m for inquests and investigations. Since 1990, the number of deaths has doubled.
The PCA report, Deaths in Custody: reducing the risks, says: "Any such failure to learn from previous experience will cause problems for managers in the police service once the Human Rights Act comes into force in the year 2000. A court would then be entitled to consider whether proper steps had been taken to improve procedures which had clearly failed to protect life in the past."
It adds: "Having now had four years' experience of supervising nearly 50 investigations a year, the authority is starting to see the circumstances of tragedies being repeated. It is not just that deaths are occurring for the second time in the same police station. In some cases, the death has followed an identical pattern."
Peter Moorhouse, chairman of the PCA, said the authority had supervised investigations into almost 250 deaths in five years. "As our experience has grown so has our concern. We believe that a number of these deaths could have been prevented."
The effects of alcohol and drugs account for the highest proportion of deaths in custody - making up two in five fatalities. Some form of heart failure accounted for more than one-quarter and one in four deaths were suicide.
While many of the most high-profile cases involve black men in custody, often linked to a violent struggle with police officers, non-whites only make up 14 per cent of all fatalities.
Recommendations made by the PCA to prevent repeat deaths include keeping cell hatches closed to prevent people using them to attach a ligature for a suicide attempt, ensuring that detainees are regularly checked and have not fallen unconscious and greater use of closed-circuit television in cells. Regular training for officers in the use of batons and making sure they do not use dangerous neckholds during arrest are also listed. "Better first aid skills could result in lives being saved," it adds.
An on-going review is expected to lead to the police being forced to provide bereaved families and lawyers with information about a death in custody before the inquest.