Research for the commission - set up in the wake of a series of grave miscarriages of justice - has found that detective constables can too easily be sucked into a 'macho and elitist' CID culture suspicious of outsiders and believing that rules are there 'to be bent'. They are left largely unsupervised, are generally 'trusted to get on with it' by their superiors, and they are under far too much 'pressure for results'.
While acknowledging that some legislation - like the Police and Criminal Evidence Act - and other initiatives had afforded suspects some greater protection, the chance for sloppiness and malpractice which could result in miscarriages of justice remained because current policing methods were open to abuse.
The study calls for the introduction of independent 'quality control units' within each police force. These could subject any officer or investigation to random checking, and instigate disciplinary or criminal proceedings if malpractice was uncovered. The authors say this would 'ensure integrity can be demonstrated rather than assumed'.
Although this is unlikely to satisfy many reformers - including Cardinal Basil Hume and Lord Scarman - who have called for total independent supervision of all investigations, it may find favour with a commission conscious of Treasury restrictions.
The study involved interviews with detectives of all ranks, observation of their activities and examination of documents. It concentrated on three forces - two metropolitan and one large county, not identified.
It also calls for better training programmes which highlight miscarriages of justice and the part played by police; greater links between uniformed officers and detectives, and a search for new investigative strategies which are less dependent on confessions.
The researchers had looked for the 'worst possible scenario', but said that did not imply bad behaviour was commonplace.
A spokesman for the Police Federation, which represents the rank and file, said he could not comment until the report had been considered thoroughly.
The Conduct and Supervision of Criminal Investigations: Royal Commission on Criminal Justice Research; Mike Maguire and Clive Norris; HMSO; pounds 15.50.