A new speed camera is being tested in south-west London in an attempt to prove its value to the Government.
The German machine, made by a company called Robot Visual Systems, measures the average speed of cars rather than their miles per hour at one fixed point.
The Association of British Drivers has dismissed the new type of camera as "the very worst incarnation of speed cameras".
A London Safety Camera Partnership (LSCP) spokesperson said: "Transport for London is facilitating a trial of average speed camera technology on the A3 near Kingston.
"This is purely a technology trial and the cameras are not enforcing. It is essential that we trial measures that could be used to enforce speed limits and reduce casualties."
Nigel Humphries, from the Association of British Drivers, said they are only "marginally" effective when used on motorways during roadworks to force people to drive at the same speed. They don't deal with an accident black spot.
"An average speed camera makes people put cruise control on and not think about what they're doing."
Other manufacturers of average speed cameras have already tested their models in Scotland, the Midlands and in north London.
© Press Association 2008