Coming soon: The speed camera you cannot beat

The digital cameras can operate round the clock as they require no film and can photograph the driver's face as well as number plates.

So the first a speeding driver would know about being caught is when a £60 fine popped through their letter box.

Campaigners claim the cameras, which are smaller and less easy to spot than the old-style units, are 'cash cows' that will do little to make roads safer.

Paul Smith, of the Safe Speed road safety campaign, said: "The fact that you do not know you have been flashed adds more uncertainty, which is never a good thing for safety.

"But a cosmetic makeover won't disguise the reality that the Government's speed camera policy is a failure."

A trial on the A4 Great West Road in London has already trapped drivers but they will not be prosecuted as the camera has not been officially approved.

Once they have been sanctioned by the Government, the devices are expected to be installed across the country.

The new device can be used forward or rear-facing so they can also trap speeding motorcycles, which only have number plates on the back.

The cameras, which can operate on battery power in case of a power cut, rely on wireless technology to send digital images to police so that the details can be processed quickly.

They can also be used to catch drivers who jump red lights.

Its makers, Truvelo, were given permission to test the camera at Gillette Corner, Isleworth, by Transport for London and is working with the London Safety Camera Partnership (LSCP).

A TfL spokesman said the trial was "openended" and would continue until the device was approved by the Home Office.

The number of people killed or seriously injured on London's roads has fallen by 41 per cent since the mid-nineties.

TfL says cameras have played an important role in reducing the number of casualties, together with other road safety measures such as 20 mph zones, as well as advertising and educational initiatives.

About half of all motorists flashed by speed cameras in London avoid a fine.

This compares with a 100 per cent "hit rate" in areas including Kent, Hertfordshire and Bedfordshire, and a national rate of around 60 per cent.

All major speed camera firms - including Truvelo, Serco's Gatso, RedSpeed and Robot - have commissioned newlook cameras from Crown UK which designs and manufactures the devices.

Crown UK has sold more than 7,500 housings worldwide - 6,000 of them in the UK. The UK's network of cameras catches an estimated two million speeders each year and the number of drivers with penalty points exceeds six million.