A new type of speed camera that does not flash and requires no film is being tested in west London.
The "d-cam" can photograph drivers' faces and number plates
The digital speed camera or "d-cam" photographs drivers' faces and number plates and, if it wins Home Office approval, could be used nationwide.
TfL (Transport for London) has tested it on London's A4 Great West Road since April. It detected speeding drivers but no fines are being issued in the trial.
Anti-speed camera group Safe Speed said the new cameras would confuse drivers.
Developed by west London firm Truvelo, the new digital speed and red light camera does not flash to alert drivers when it photographs speeding vehicles.
A TfL spokesman said the number of people killed or seriously injured on London's roads has been reduced by 41% since the mid to late-1990s.
"Safety cameras have played an important role, along with other road safety measures such as 20mph zones, advertising and educational initiatives," he added.
But Safe Speed founder Paul Smith said: "The speed camera programme has failed to improve road safety."
Speed cameras "are designed to make money for the companies who manufacture them", he added.
"These new cameras will leave drivers less certain, and that's another bad side effect."