The number of cases where criminals were jailed fell last year, according to figures released yesterday.

The Criminal Proceedings in Scottish Courts figures, published by the Scottish Executive, showed fewer than 16,000 custodial sentences were imposed in 2005-06 - down 4% from the previous year.

However, more than 80% of these sentences were for six months or less and there was also a fall in the number of community sentences handed out, leading critics of the executive's policy on sentencing to demand a rethink.

In 2005-06, there were just fewer than 16,500 community sentences, such as probation orders and community service orders, imposed on offenders - down 3% from the previous year. It is the second year in a row there had been more community sentences than custodial sentences imposed.

Referring to the large number of short sentences, SNP justice spokesman Kenny MacAskill said: "It's time for a credible and coherent prison policy that locks up dangerous offenders and deals with petty offenders in the community."

He said rather than "filling prisons with minor offenders", the SNP would ensure jails were used to punish the dangerous criminals and those who had committed serious offences.

Scottish Conservative leader Annabel Goldie said: "These figures are indicative that people do not have to prove they deserve bail, it is virtually gift-wrapped. Quite simply, that should not be the case. Crime and offences are on the increase and we are losing the war against criminals and drugs."

Susan Matheson, chief executive of Sacro, Scotland's leading community safety charity, said: "Yet again, we have over 80% of custodial sentences being very, very short and instead of kicking their heels in prison for a few weeks, people would be better to be on a community disposal that's really rigorous and challenging and changes their attitude to offending."

The figures showed the courts dealt with criminal cases involving 142,200 people last year - down 5% from last year and 19% below the 174,500 recorded in 1996-97 - resulting in 128,400 convictions.

The average fine handed out to individual offenders last year was £212, with compensation orders averaging £281.

The figures also showed 25,600 offences, 14% of the total proved in court, were committed while the person was on bail, the first time these figures were included.

There were a total of 545,900 penalty charge notices for parking infringements in the council areas operating civil penalty schemes - Aberdeen, Edinburgh, Dundee, Glasgow, Perth and Kinross and South Lanarkshire.

Money raised from these and from towing away ille-gally parked cars raised £16.9m in 2005-06, compared with £14.4m the previous year.

The figures come six months after Justice Minister Cathy Jamieson announced Scotland would need the equivalent of one new large prison and up to £67m a year to bring in the executive's get-tough policy on sentences.

She published a bill that will mean more prisoners serving longer sentences and a shake-up of social work and electronic tagging.

The move would be on top of a record prison population last year of more than 7000 inmates in most weeks, causing serious concern to prison inspectors. Scotland is close to the top of Europe's league for locking up people.