Mr FitzPatrick has promised to make the issue a priority in the wake of public indignation over some recent cases. The SNP member at Holyrood was staggered to learn the Justice Department at the Scottish Executive has no idea of the numbers of prisoners who are released early and then go on to re-offend.

Mr FitzPatrick said, “This is incredible. So we have no way of knowing what problems are associated with people on early release before their rehabilitation is completed, or even whether the system is working properly.

“Our position is that I will be asking for a full review of sentencing, and we are certainly, as a party, opposed to automatic early release because that does not make sense.

“If people are sentenced there is a reason for it, and it makes no sense to then say your sentence will be shorter.

“I hope this is something an SNP-led executive would be able to take forward quickly and I will be speaking to the appropriate Minister on Thursday.”

The disclosure about the lack of figures and knowledge comes in the wake of several high-profile cases this year that have alarmed and outraged police and parliamentarians alike.

One case involved the early release of a civil servant who carried out a cocaine-fuelled knife attack on Dundee police officers.

He was let out after serving only four months of a year’s sentence.

Earlier this year there was another case that prompted dismay — that of a prolific housebreaker, from Dundee, who had broken the law only two months after an early release.

He had been placed on an electronically-tagged home curfew when he re-offended after serving only a quarter of his 20-month sentence

Victim Support Scotland, which represents victims of crime, and rank and file police officers condemned the system of early release and insisted it was time for a review, particularly for crimes involving assaults on emergency service personnel.

A Victim Support spokesman said a sentence should match the crime, and called for a major debate in Holyrood on whether a sentence should mean what it says.

A Justice Department spokesperson said that, generally, prisoners facing up to four years in jail would be automatically released after serving half their sentence.

There were variations, including people who had already served remand time who would be released even earlier, plus the home curfew release programme.