Ministers have been urged to all but ban jail sentences of under one year in a radical move that would slash the prison population and help pay for a policy of keeping dangerous criminals behind bars for longer.

The Scottish Government has quietly announced that it will launch a formal consultation on extending an existing presumption against sentences of up to three months in length, which was introduced controversially in 2010 amid claims it would halt a custodial "revolving door" but in practice has made very little impact.

Justice Secretary Michael Matheson signalled the move as part of wider reforms designed to reduce the number of criminals being punished with jail time.

The MSP is planning to increase use of community-based sentences and launch a series of trials to test methods of reducing short jail terms - which the SNP administration candidly admit "don't work".

While the Government refused to be drawn on the length of time it was considering extending the presumption against short sentences to, experts warned that only a 12 month period - linked to the maximum powers in less serious cases - would prove effective.

Cyrus Tata, Professor of Law and Criminal Justice at the University of Strathclyde, said: "Rather than using the number of months, it would be better to specify the kinds of offences that would normally be non-imprisonable. But if the number of months is the only tool in the box, it would need to be consistent with summary powers, currently 12 months, to have any real impact."

The suggestion will encounter strong opposition in some quarters and if pursued, lead to accusations of being soft on crime. The issue is likely to be seen as a test of Mr Matheson's claim that he wants to build "the most progressive justice system in Europe".

A move to 12 months would bring Scotland into line with Belgium which recently scrapped jail sentences of under one year. Its justice minister branded them "a try-out in jail" that increased reoffending rates.

This week, Mr Matheson pushed through proposals to extend the length of time criminals on long-term sentences will spend behind bars, with a new law to restrict periods of mandatory community supervision to just six months. Previously, automatic release came at the two-thirds point for those serving four years or more.

The Justice Secretary has suggested a bill that will rise to £17 million a year will be paid for by reducing the number of short sentences handed out but until now had not set out his plan to achieve the aim.

Before it introduced its presumption against three-month sentences, a then-minority SNP Government initially argued for a six-month period but watered down its plan following a backlash. The three month provision eventually passed with just three votes, relying of support from Liberal Democrats and Greens.

However, with an SNP majority at Holyrood and a commanding position in the polls heading into next year's election, Mr Matheson is in a better position to push ahead with far-reaching reforms after independent researchers found "little evidence" that the three month presumption featured "prominently or explicitly" in sheriffs' decision-making when sentencing.

The most recent figures show an average daily prison population of 7,579 this year - eight per cent higher than 2006. The average jail sentence is around nine months long.

Green co-convenor Patrick Harvie said: "Anyone who's really dangerous enough to require imprisonment is unlikely to have their offending behaviour successfully challenged in the very short time that rehabilitation services will have to work with them."

Scottish Conservatives spokeswoman, Margaret Mitchell, said a lack of resources meant that community sentences could not be properly monitored.