Technical and legal difficulties have prevented the Highways Agency from switching on the network of 36 new digital cameras intended to enforce variable speed limits on the London orbital motorway.
The failure was discovered by the AOL website, which had hoped to identify the biggest money raiser on the 117-mile long road, only to find that the cameras had caught no speeders at all.
Safety groups condemned “incompetence” by the agency, which owns the cameras although enforcement is handled by police forces along the route.
With around 500,000 drivers using the M25 every day, it is one of Europe’s busiest motorways. Cameras have been used to catch speeding drivers on it since 1995, and the network has grown during the intervening years.
They are supplemented by police patrols, which continue to enforce the limit, even if the overhead cameras do not.

I doubt its possible to break the speed limit on the M25

A good portion of the speed cameras in the country are shells anyway. We had one outside a former workplace - all the locals knew it was empty and they all ignored it. It was replaced with an identical functioning model after a couple of years (or they just put the guts in it) and it caught half the village in a couple of weeks! I think it was filled with builders foam shortly afterwards.

In which case it becomes a cash generator. Empty boxes just encourage people to break the law and if people one they will slam the breaks on and become a greater risk.

BRAKES!

Brain not in gear.

Is Foreign English your first/native language?

I doubt its possible to break the speed limit on the M25

Oh it is with the variable speed zones. You often see them on, even when there's little traffic, saying something like:
60 - 60 - 60 - 60 - 40 - 60 - 60.
You know they're waiting to catch people out with the odd random low limit with the rest.