Police have issued a warning after thieves targeted seven cars at the weekend.

Catalytic converters were stolen from seven cars overnight between Friday and Saturday - mainly in Borehamwood and Bushey.

The vehicles targeted were Lexus models and Toyota's, specifically the Prius and Auris models.

Catalytic converter thefts have increased this year due to the precious metals they contain and the high metal prices, with thieves even trying to steal them on the roadside and in car parks, sometimes in daylight.

Hertsmere Safer Neighbourhood Inspector Rachael Robertson said: "This number of offences is obviously of concern and it’s something we are working to tackle, including carrying out additional patrols in hotspot areas. If your catalytic converter is stolen it renders your car almost undrivable and can be incredibly costly to repair and replace.

"This summer, Hertfordshire Constabulary launched a new campaign, Operation Feline, to help drivers protect their catalytic converters and to deter thieves. As part of the campaign certain garages across the county are offering a free security marking service and I’d urge residents to take up this offer.

"We would also urge the public to follow our advice, remain vigilant and report incidents of suspected catalytic converter theft, particularly where people are trying to get under cars in public car parks or on public roads. If you see this happening, please call 999 immediately."

Garages carrying out free catalytic converter marking in Hertsmere include Kwik Fit in Borehamwood, and JTT Autotech and C &C Motors in Potters Bar.

Details of the security marking scheme and further garages taking part in the county, can be found at www.herts.police.uk/operationfeline.

Police have issued the following advice to drivers

• Lock your car whenever it is left unattended and keep it in a garage when parked at night if possible.

• When using a garage is not possible, park close to fences, walls or a kerb with the exhaust being closest to the fence, wall or kerb to make theft difficult.

• Consider fitting CCTV on your home or driveway, to help deter thieves.

• Use PIR or LED security lighting to make your vehicle more visible and this can also act as a deterrent.

• If your catalytic converter is bolted on, consider having the bolts welded to make removal difficult.

• Fit protective coverings on catalytic converters, such as the Toyota manufactured CATLOC device, (these are made for Toyota Prius made between 2004 and 2009) as these can make it much more difficult for thieves.

• Have your catalytic converter etched or forensically marked, and put stickers in the windscreen to say this has been done.

• Look for car parks with a Secured Car Park sign which have recognised levels of security. If you have a garage at home, ensure you use it and lock it properly.

• Noisy gravel on your drive can help deter a would-be thief, as they don't want to alert you to their approach.

• Never leave valuable items or tools on display in your vehicle as this may encourage a thief to break in.