The rising price of metal is causing an increase of catalytic converter thefts in the district.
Hertfordshire Constabulary is working with M Wilson Motor Repairs to offer drivers of diesel cars and light commercial vehicles free catalytic converter marking.
Marking the converters, which turn pollutant gases into less harmful ones, makes it much easier for the police to trace where it came from.
Inspector Paul Lawrence of the Crime Reduction Unit said: "The theft of catalytic converters has been a recurring problem over the last couple of years, particularly from diesel vans as they are easier to access on high clearance vehicles.
"Thieves target the units for the precious metals they contain.
"Marking the converters makes them much less appealing to thieves as they can easily be traced back to where they were stolen from.
"Scrap metal dealers are now required to record who they buy their scrap from, meaning we have a good chance of catching the person that stole the unit if it is marked."
Owners of diesel cars and light goods vans up to 4,500 kgs gross vehicle weight can visit the garage on Campfield Road from Monday, April 20 for two weeks.
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