PRISONERS serving jail terms of more than four years will no longer be eligible for automatic early release.

The move will mean hundreds more of the country's most serious offenders will not be released automatically after two-thirds of their jail term, as is the current situation.

Announcing the change, the First Minister said a guaranteed period of post-jail supervision would be put in place. The safeguard followed concerns by criminal justice experts that the public would be placed at greater danger if, as at present, offenders serving out their full sentences were released "cold". MSPs were warned some criminals preferred to "max out" their sentence in order to avoid supervision on their release.

Under existing legislation, long term prisoners - defined as those serving more than four years - can apply for parole halfway through their sentences but are released automatically after two-thirds of their jail term.

MSPs are considering the Scottish Government's Prisoners (Control of Release) (Scotland) Bill which was intended to end automatic early release for sex offenders serving four years and all other criminals jailed for 10.

Announcing the bill will be tightened, Ms Sturgeon said prison remained "the most appropriate place for serious offenders".

She added: "We recognise that tough action is required to tackle those offenders who commit the most serious crimes, ensuring that communities are kept safe while at the same time making efforts to reduce the likelihood of reoffending."

The new post-jail period of supervision will be set by the courts as part of an offender's sentence.

The move was Victim Support Scotland.

Susan Gallagher, acting chief executive, said: "For those who live in all of the communities in which we work this should be viewed as a step closer to achieving a system in which sentences are straightforward and understandable to the victim and those communities."

However the Conservatives said the changes did not go far enough.

Scots Tory chief whip John Lamont said: "This is clearly welcome news but it still falls short of what the SNP has been promising to do since first getting elected in 2007.

"It will still mean that 97 per cent of prisoners will be automatically released from prison half way through their sentence, no questions asked.

"Automatic early release of prisoners is an insult to victims and makes a mockery of our justice system. Despite the announcement today, the vast majority of offenders will continue to enjoy the benefits of our soft touch justice system."

Last year, just over 14,000 offenders were sent to jail in Scotland, of whom 450 received sentences of more than four years.

Previous attempts to end automatic early release have raised concerns about increasing pressure on Scotland's crowded prisons.

However, it is expected the latest move will increase the total prison population by about 400 over 10 years.

Last week there were 7,474 offenders behind bars, a figure within the overall prison capacity of 8,159.

Dr Cyrus Tata, professor of law and criminal justice at Strathclyde University, who criticised plans to extend early release when he appeared before a committee of MSPs earlier this year, said sentences should be made clearer.

He said: "Successive governments have failed to work out a coherent and publicly defensible reform of early release from prison because they've dealt with it in a piecemeal way.

"The only way to produce a coherent and publicly defensible policy is to examine at the same time both sentencing and release so as to work out an integrated joined-up policy."