Scotland's courts are locking up a higher proportion of shoplifters than sex offenders as the prison population reaches crisis point.

Research by Professor Alec Spencer, former head of rehabilitation at the Scottish Prison Service (SPS), has revealed that some 29% of shoplifters were sent to prison, compared to 27% of those charged with indecency.

The most up-to-date figures show that, of 837 crimes of indecency including rape and indecent assault in 2005-06, 27% were sent to prison, some 30% were given community sentences and one-quarter got a fine.

In contrast, of 7928 offenders prosecuted for shoplifting, some 29% went to prison, 19% were given a community sentence and 35% were fined. The remaining figures may be explained by those who were acquitted.

Mr Spencer said: "This seems completely ridiculous. To lock up more shoplifters than sex offenders is all the wrong way around. Locking people up does not solve crime.

"What we need to do is cut the prison population and invest more in education and literacy rather than locking people up for short sentences that do nothing to address their behaviour.

"Judges get frustrated with repeat offenders and the shoplifters may have been given very short sentences, but that is part of the problem, clogging up the prisons. Some 8603 people were sent to prison last year for six months or less and this is just a huge waste of time and money."

More than one-third of the women in prison are there on theft charges.

The revelation comes as new figures obtained by The Herald show a 6% increase in remand numbers early this year compared to the same period in 2007.

Despite unprecedented attempts by ministers to reduce prisoner numbers, Scotland's remand population has increased significantly. Sheriffs and officials have said the increase is partly a result of new legislation introduced by the Scottish Government in December.

Despite prison overcrowding being at "crisis" levels according to Alex Salmond, the First Minister, regulations on bail were tightened significantly in December, causing an even faster rise in the numbers of untried inmates behind bars.

On Friday, May 16, this year the total remand population in Scotland was 1643 as compared to 1546 on Friday, May 25, last year. March and April saw similar increases.

Officials warned that the tightening of bail regulations under the Criminal Proceedings etc (Reform) (Scotland) Act 2007, which came into force in December, would increase dramatically the already burgeoning remand population.

Partly as a result of the new regulations, which place the onus on the sheriff to give reasons for not granting bail rather than there being an assumption of bail unless it was opposed by the Crown, officials say prisons are now even more overcrowded.

The recent Audit Scotland report on prisons found that the prison population has increased by more than one-fifth since 2001 and that the biggest rise has been in the remand population which, on average, has increased some 78%, from 881 in 2001 to 1567 this year.

A spokeswoman for the Scottish Government said: "Sentencing in individual cases is a matter for the courts and the sheriff who is in possession of the full facts of the case.

"The independence of the judiciary is a fundamental cornerstone of the Scottish criminal justice system and we attach great importance to judicial discretion in individual sentencing decisions.

"However, we do believe that there is a case for sentencing guidelines to help deliver more consistent and transparent sentencing, and improve public confidence in the criminal justice system.

"We therefore plan to hold further consultation and dialogue with key interests, principally the judiciary, on how to achieve this, including the arguments for the creation of a statutory Sentencing Council.

"Clearly, the decision whether an accused is bailed or remanded is for the court to make."