The system, called Tracker, has the approval of the Home Office and the police, who are anxious to increase the chances of recovering stolen vehicles. More than a third of the 630,000 vehicles stolen last year have not been recovered and the number of thefts by professional thieves who aim to retain or sell the car has been increasing.
Subscribers to the system, which is available only from the AA, will pay pounds 160 plus an annual subscription of pounds 61.10 to have a device fitted to their vehicle. If the vehicle is stolen, the owner reports the theft to the police and the Tracker control centre.
The device in the car will then be activated to emit radio signals. Police cars - and possibly fixed locations such as ports and estuary crossings - fitted with computers that detect the signal will then be able to trace it.
As a car fitted with a detection device comes within one to three miles (in an urban area) of the stolen car, the computer indicates the radio signal's direction.
The makers claim that the unit is concealed within the fabric of the car and is 'virtually impossible to remove without knowledge of its exact location'. The unit will also power itself for a while if the battery is disconnected, and should last as long as the car. There are no outside signs such as stickers or aerials.
Several insurance companies are offering discounts to motorists who fit Tracker.
The system has proved itself in the United States. Since its introduction in 1986, all but 6 per cent of stolen vehicles fitted with the system have been recovered. The average recovery time in the US is claimed to be two hours.
Police said yesterday that the theft of car telephones amounted to pounds 50m a year. Representatives from the police, manufacturers Motorola, Cellnet and the Federation of Communication Services met in Slough, Berkshire, to discuss the thefts.