Proposals to lock up 'dangerous people with severe personality disorder' indefinitely are 'fundamentally flawed', according to mental health experts.
Health secretary Frank Dobson and home secretary Jack Straw put forward two options for public consultation on Monday.
One provides for a new legal framework under which 'DSPD individuals' would be held in new facilities outside the prison and health services.
A less drastic measure would 'strengthen' existing legislation by holding those judged to be a danger in prison or hospital.
Ray Rowden, visiting professor at York University, said the measures would prevent the most dangerous individuals - 'the loners' - from seeking help.
The former chief executive of the High-Security Psychiatric Services Commissioning Board added: 'Who would come forward and say what they are intending to do when they could end up being banged up?
'I might feel a bit more comfortable about this if the science was better but there is no consensus about what we mean by severe personality disorder, ' Professor Rowden said.
Alan Franey, former chief executive of Broadmoor Special Hospital, said the report did 'not appear to address how new institutions would be staffed'.
He was also 'very dubious' about how a 'third service' would provide proper accountability.
'I am a bit puzzled - if it is not part of the health service and not part of the prison service then what is it part of?' he asked.
The report admits that cutting the number of serious crimes by 200 a year 'would be achieved at a cost of doubling the average period in detention from five to 10 years'.
Mind and the National Schizophrenia Fellowship also expressed concern. NSF urged the government not to create 'a cheap dumping ground' for DSPD patients.
Launching the document, Mr Dobson described current systems as 'indefensible', providing 'little more than a lottery' in terms of effective treatment offered.
The report estimates that up to 2,500 people would be affected by the measures, of whom 1,400 are currently in prison, 400 in secure hospitals and the rest in the community.
Mr Straw insisted that the 'random nature of their potential violence' distinguished DSPD individuals from 'the common criminal'.
Managing Dangerous People with Severe Personality Disorder: proposals for policy development. www.dph.gov.uk