A NEW law which the SNP said would end automatic early release of prisoners may be watered down further, after a veteran MSP said that a Government u-turn had not gone far enough.

The Scottish Government had pledged to stop criminals serving long sentences being released automatically, meaning some would spend every day of their term behind bars.

However, after concern was raised that the move would see some set free with no supervision or support making them more dangerous, Justice Secretary Michael Matheson backed down and instead proposed automatic release six months early.

The revised plan was attacked by experts on community rehabilitation who said that while it was an improvement on initial proposals, the six month period was too short and that the mandatory release phase should be linked to the length of sentence.

Labour MSP Elaine Murray, deputy convenor of Holyrood's Justice Committee, has put forward an amendment which would instead see prisoners released when they have 12.5 per cent of their sentence left to serve. It would mean that someone serving a four year sentence would be let out six months early, while a prisoner serving 10 years would be released after eight years nine months.

Ms Murray said: "It stands to reason that if you're in prison longer, it takes longer for reintegration. The recommendation from the committee [in its stage one report] was that the period should be proportional to the length of sentence.

"It's important to acknowledge that the Government is no longer getting rid of automatic early release. I think Michael Matheson has been left with a mess in what was always Kenny MacAskill's Bill."

If Ms Murray wins a vote in the committee today her amendment will be included in the Bill. However, the Government would have the opportunity to amend it further at stage three, when MSPs will decide whether the Control of Release Bill will become law. Mr Matheson will also be present to move his amendments, which would see the blanket six months brought in. The committee is made up of four SNP members, two Labour, one LibDem, one Tory and one independent.

At an evidence session last week, Fergus McNeill, Professor of Criminology and Social Work at the University of Glasgow and Cyrus Tata, Professor of Law and Criminal Justice at the University of Strathclyde, agreed that at least a quarter of sentences should be served in the community arguing it was necessary for effective reintegration that would protect the public from further offending.

Reacting to the suggested 12.5 per cent period, Professor McNeill said: "I think 25 per cent would be much better, but this would at least mean that the reform was proportionate across the full range of determinate sentences. That is better both from the point of view of justice and resettlement."

Currently, those sentenced to four years or more are released two thirds of the way into their sentence, serving the remainder in the community under supervision but subject to recall to jail if they do not follow strict conditions.

Professor Tata said: "It's good to see a move towards proportionality, which is important in terms of justice and public safety. But there is a real danger that 12.5 per cent will be insufficient to supervise a long term prisoner released into the community."

Tory justice spokeswoman Margaret Mitchell, also an experienced MSP who sits on the committee, has put forward her own amendment which would delay the plan.

She said: "This legislation is fundamentally flawed and its effects won't be felt for some years. We have to make sure we end up with something that is clear and consistent, not a dog's breakfast.

"We want to see the end of automatic early release for all prisoners - that has been our position for some time. As such we will be moving to postpone these particular plans and revisit them following further scrutiny of Criminal Justice Bill later this year."

A government spokeswoman said: "Our position on the Control of Release Bill will be set out at the Justice Committee, when the Cabinet Secretary for Justice speaks in support of our policy of guaranteed mandatory supervision of six months."