A spokesman for the...

A spokesman for the Department for Transport explained: "The police have the right to carry out covert surveillance. Devices that detect the signal given off by a mobile speed camera can give this away, and this could be seen to affect the police"s ability to do their job properly." But he added: "We have no problem with those systems which only use GPS satellite technology."

Such gadgets, known as locators, are deemed acceptable as they can only tell drivers where fixed cameras are - and this information already exists in the public domain. In addition, Gatsos are designed to slow motorists at accident hotspots, and GPS systems help warn drivers that they"re nearing a high-risk location.

Many European countries - including France - have already banned all detectors, but a similar move by the UK authorities could give weight to the argument that Gatsos are no more than a way of raising revenue.