Tens of thousands of murderers, rapists and violent criminals could escape prosecution following a legal ruling which has left police "running round like headless chickens", a chief constable has said.
The ruling, which was made by a district judge and backed by a judicial review in the High Court, means officers will no longer be able to bail suspects for more than four days without either charging or releasing them.
It challenges an interpretation of the law which has been used for the last 25 years and means releasing suspects on bail and calling them back for questioning weeks later - a common practice in most major inquiries - is "pretty much a dead duck".
Home Secretary Theresa May said the decision was a "matter of great concern", adding: "We are conscious of the concerns this judgment has brought in terms of operational policing."
The Government, along with both the Association of Chief Police Officers and the Crown Prosecution Service, are considering the ramifications for police across England and Wales, she said. Police are seeking leave to appeal to the Supreme Court while the Home Office is looking into whether or not it is necessary to introduce legislation to address the issue.
Sir Norman Bettison, chief constable of West Yorkshire Police, said: "It's on the verge of a disaster now because the question being asked by my custody sergeants is, 'What do we do, boss?' I cannot countenance turning people away from the charge office and telling them all bets are off and they are free to go."
He went on: "We are running round like headless chickens this morning wondering what this means to the nature of justice."
A Scotland Yard spokesman said: "This ruling is significant in that it fundamentally changes the way the legal system has applied Pace (Police and Criminal Evidence Act) for 25 years. The Metropolitan Police Service has sought senior legal advice and has worked with the Home Office and the CPS to understand the implications of this case. We have now issued advice accordingly."
That advice, sent to all chief officers in England and Wales, stated that the effect of the new ruling will "need to be reflected in the way in which any case is investigated, particularly once a decision is made to arrest".
It made clear that the pre-charge detention limit is now a maximum of four days, running from the time of arrest, at which point the suspect must be released or charged. The suspect can not then be rearrested unless there is new evidence, the guidance said. But it is also continuing to arrest suspects and release them on bail for several weeks.