Fleets using GPS tracking systems have been warned that these may not always help recover stolen vehicles.

According to Tracker, which uses the rival VHF system, GPS systems are more susceptible to ‘jamming’ devices used by thieves.

Mark Walls of Tracker said: “Jamming is a technique used by thieves to block the satellite signal to the GPS receiver, or prevent GSM-based communication with the tracking device, making it impossible to trace a stolen vehicle. Whilst GPS/GSM devices have their place in stolen vehicle recovery, there really shouldn’t be sole reliance on this technology.”

However, director of in-vehicle products for Trackstar, which uses GPS technology, Pat Gallagher, said: “Trackstar has a 90% recovery rate, which we believe is the highest recovery rate in the industry. We have seen no evidence of an increased use of jamming devices and in fact both Thatcham and the police assure us that they do not see jamming devices as a concern.”