While there has been a reduction in accidents in west London, where a demonstration project was introduced two years ago, the rate has begun rising again as drivers become blase about the cameras.
Yesterday, while unveiling the 300th camera site in London, Steven Norris, the road safety minister, said cameras had proved effective "in deterring speed in areas that in the past have suffered too many unnecessary accidents".
Figures from the west London project show that fatal accidents have reduced from 23 per year before the installation of cameras to 7 per year afterwards. Similarly, serious casualties are down from 271 to 233.
However, when the statistics are examined on an annual basis, they show that the year before the cameras were introduced, there were 1,267 accidents. This went down to 1,015 the following year, but rose again to 1,161 last year.
In terms of the number of casualties, the figures for the three years are 1,661, 1,324 and 1,544; showing that the rate is nearly back up to the level it was before the cameras were installed.
The police admitted, too, that there had been a 45 per cent increase in accidents caused by cars being driven too close to the vehicle in front, as a result of all traffic slowing down for the cameras, which are all clearly signposted.
Mr Norris rejected suggestions that the deterrent effect on motorists reduced as they became familiar with the location of sites, but admitted: "The results won't go on plunging as they first did."
"Familiarity breeds a certain contempt in all these things and the idea that road safety measures decrease in their success over time is one we are all aware of," the minister said.
Although there are 300 sites around London, many have only dummy equipment since the actual cameras cost pounds 27,000 each and the Metropolitan Police says it cannot afford to have a camera permanently in every box.
The dummy cameras still flash as if they were fully functioning and therefore still act as a deterrent. Almost 15,000 people were prosecuted last year for speeding offences after they were caught by the cameras. Each received a pounds 40 fine and three points on their licence.
Edmund King, campaigns manager for the Royal Automobile Club, welcomed the reduction in accidents but warned that too many prosecutions might result in people not taking speeding seriously.
"With so many speeding fines being issued automatically, people are treating them a bit like parking tickets," Mr King said.
"The cameras should be concentrated at junctions and at accident blackspots, but some of them are on straight stretches of dual carriageway, which is ridiculous."Reuse content