Doctors and patients' organisations yesterday condemned new proposals from the Government to lock up severely mentally ill people before they have committed an offence.

Doctors and patients' organisations yesterday condemned new proposals from the Government to lock up severely mentally ill people before they have committed an offence.

Ministers said the draft mental health Bill, the second to be produced in two years, would provide better protection for the public and patients, but it drew a storm of protest. The Mental Health Alliance, representing 60 patient and carer groups, said it was "unfit for the 21st century" and would deter thousands from seeking help. The Royal College of Psychiatrists said it was "unfair, stigmatising and dangerous".

The Bill seeks to protect the public by ensuring people with dangerous severe personality disorders receive compulsory treatment, while providing safeguards for patients who may be detained against their will. It is a revised version of a draft first published in June 2002, which drew widespread criticism.

It was triggered by the case of Michael Stone, convicted for the murders of Lin and Megan Russell and the attempted murder of Josie Russell in a hammer attack in 1996. Stone, whose second appeal started and was adjourned yesterday until 15 October for legal reasons, had been discharged from a mental hospital shortly before the killings.

The new version of the Bill, the biggest reform of mental health legislation in 50 years, contains concessions to critics of the first draft and is couched in language that shifts the focus from protecting the public to meeting patients' needs, but the most controversial section remains. It seeks to close a "loophole" in the existing legislation whereby patients may only be detained if they are considered treatable.

Psychiatrists have regarded some people with dangerous severe personality disorders as "bad" rather than "mad", refusing to detain them on the ground they are untreatable and it would cast them in the role of jailers.

The first version of the new Bill sought to remove the "treatability test" but critics complained the criteria for who should be detained were cast too wide. Yesterday's revised version narrows the definition to include only those at serious risk of suicide or self-neglect, or of harming others, and contains a provision that patients only be detained where treatment is "clinically appropriate".

Rosie Winterton, a Health minister, said: "The Bill means that the small minority of people with mental health problems who need to be treated against their wishes, normally for their own protection but occasionally for the protection of the public, will get the right treatment at the right time."

Tony Zsigmond, of the Royal College of Psychiatrists, rejected Ms Winterton's argument. "This Bill will increase the number of people whom we 'jail'," he said. "It is authoritarian and coercive."

Andrew McCulloch, the chief executive of the Mental Health Foundation, said the Bill "stigmatises and marginalises people with mental health problems" and was a "shameful step backwards". He said psychiatrists might be unable to resist pressure from the public to detain patients.

Angela Greatley, the chief executive of the Sainsbury Centre for Mental Health, said that it would place psychiatrists and social workers under pressure to "detain many more people and compel them to take treatments that do not benefit them."

The Government has referred the Bill to a cross-party committee of MPs and peers "because of its complex nature". The health department said 900 additional staff, including 130 psychiatrists, would be needed to implement it and £2.5m would be spent over the next five years on research.