AMSTERDAM, Saturday - Locking up junkies and illegal immigrants that fill their day with theft and break-ins for two years produces savings for society of no less than 4 million euros per criminal, De Telegraaf newspaper reports based on a study by the justice ministry.

From 2004, it has been possible for courts to lock up someone who commits crimes daily - a 'very active recidivist' (ZAPV-er) in the jargon - for a maximum of two years via the ISD (Incarceration of Systematic Offenders) rule, as it is known. Two researchers who were commissioned by the justice ministry to make an initial exploratory cost-benefit analysis of this rule conclude it is bearing fruit, according to De Telegraaf.

When a ZAPV-er lands up in jail for two years, this saves society 1.485 million euros in damages from crimes and violations. Additionally, the government saves no less than 624,000 euros per ZAPV-er in costs that would otherwise have been made by the red tape in all offences committed.

But even greater, claims the research, is the deterrent effect of ISD on other 'revolving-door' criminals. For each ZAPV-er locked up, 28 others step back in terms of the intensity of their criminal activities.

As against all these benefits, there is the 150,000 euros in costs of the SDE measure. A very large proportion of recidivists are addicted to heroin, often of low intelligence and suffer from psychiatric disturbances and other health problems.