GOVERNMENT plans to reform the issue of the early release of prisoners have become so muddled they now pose a threat to public safety, justice experts have warned.

The Prisoners (Control of Release) Bill, which goes to a final vote at Holyrood this week, has "changed almost beyond recognition" since it was published in August, legal critics say.

SNP ministers have rewritten it so much, and so hastily, that it no longer delivers its original aims and is fatally undermined by a lack of evidence and consultation, they claim.

The warnings are contained in a briefing being sent to all 129 MSPs ahead of the third and final stage debate on the Bill on Tuesday.

Among the groups behind the criticism are the Howard League for Penal Reform Scotland, Apex Scotland - which works with offenders - the Scottish Association of Social Workers, and Social Work Scotland.

A series of academics have also added their names to the warning: Cyrus Tata, Professor of Law and Criminal Justice at Strathclyde University, Fergus McNeill, Professor of Criminology and Social Work at Glasgow University, Prof Lesley McAra, chair of Penology at Edinburgh University, and Dr Monica Barry, a Principal Research Fellow at Strathclyde University.

Under the current system, all prisoners with determinate sentences are automatically released under licence after two-thirds of their term is served, or after half if the Parole Board judges they would not be a risk to the public.

The system has been repeatedly criticised as too lenient.

The Bill's original aim was to end automatic early release for all sex offenders sentenced to more than four years, and all other offenders sentenced to more than ten years.

However, during its passage through Holyrood, the government significantly amended the Bill to create a new regime applying to all non-life prisoners with fixed sentences over four years.

Now, all such prisoners (other than those granted discretionary parole and those subject to extended community supervision) will be released on licence just six months early.

Experts warn this blanket "mechanistic" approach gives serious offenders too little time to return safely to society under supervision, and increases the chances of reoffending.

Under the current automatic early system, all serious offenders receive at least 16 months supervision on licence.

In their briefing to MSPs, the experts warn the six-month period is a risk to public safety as it will even apply to long-term prisoners refused discretionary parole "because they have been regarded as too great a risk to public safety, or have not sought parole and resisted engaging with rehabilitative services in prison".

Although some prisoners can get help in jail and advice before their release, MSPs have heard that there are already too few courses to meet current demand.

In addition, prisoners who consider they are "subject to arbitrary detention without preparation for release" could sue the government for infringing their human rights, the critics warn.

They end by saying: "We can only draw the conclusion that this Bill does not achieve its originally stated aims.

"It will not end automatic early release, it will not reduce reoffending and it will not improve public safety in the longer term; indeed, it is likely to jeopardise both public safety and reintegration."

€ŽScottish Conservative chief whip John Lamont said: "The SNP could have made this very simple - by ending automatic early release for every prisoner. Instead, they've come up with a complete mess, and it's no wonder so many people are lining up to criticise it."

A Scottish Government spokeswoman said: "The Scottish Government has listened and responded to views during the passage of the Bill.

"The Prisoners (Control of Release) (Scotland) Bill will, if approved by Parliament, end automatic early release for all long-term prisoners with an extended sentence, and restrict automatic early release to the last six months of sentence for other long-term prisoners.

"This will help protect the public while ensuring a period of supervision in the community for all long-term prisoners leaving custody.

"The aims of the Bill are in line with the recommendations of the Scottish Prisons Commission (2008), to 'target the use of prison where it can be most effective - in punishing serious crime and protecting the public'."