Andy Evans, a Belper resident who drives to work in Wirksworth every day, said: "I think it's very underhand. I don't disagree with having speed cameras but I think they need to be visible. This suggests it is just a money making exercise.

"Hidden cameras do nothing to actually slow a speeding motorist down, they just punish them later on. The flashing signs, like the one on Kilburn Road in Belper, are much more effective at actually slowing people down.

"If they really want to clamp down on speeding then they need a highly visible presence in my opinion."

Jim Banahan, secretary of the Belper and District Road Safety Committee, said: "I don't have a problem with it really. Anything that gets people to obey the speed limit is a good thing, however I do wonder if a visible presence might be more effective.

"I would like to see greater uniformed police presence on the roads. If we were to see more police doing their jobs out on the road on motorbikes or in cars then it would help the situation more.

"It will be interesting to see if it has any impact and if a greater visible police presence could have a greater impact."

A spokesman for Derbyshire Police said: "Our fleet is made up of a range of marked and unmarked vehicles.

"Our marked and plain vehicles carry out a range of duties on our roads, including speed enforcement.

"This work is carried out on routes which are already signposted as having speed enforcement cameras sited on them and analysis has highlighted as being collision hotspots.

"Despite attempting to raise awareness and educate motorists to the dangers of excessive speeds on Derbyshire roads, there are some who continue to flout the law and put themselves and others at risk."

Tell us what you think? Are the police right to use unmarked vehicles to catch speeders?