It might get called out as a sneaky move, but safety campaigners are celebrating a decision by police forces to camouflage speed camera vans in a bid to snare motorists who flout limits.

Until now, police have used vans that might sometimes literally be spotted a mile away, thanks to their high-vis bodywork. But the bad news for speeders is they're going grey.

The first roll-out of these unmarked vans is now active in Northamptonshire, with plans for other roads, including just over the Gloucestershire border in South Gloucestershire, to join the first wave of trials.

As a low-cost, tactical change, police forces taking part in the initiative are wrapping their existing luminous orange, yellow, white and blue vans in matte grey vinyl.

The RAC said: "Police departments across the UK are able to do this as it is not a legal requirement for either local officers or councils to alert drivers about any upcoming speed cameras.

"By switching to grey vans, the hope is to stop drivers slowing down just for the police van, to just accelerate past the speed limit after the van is out of sight.

Car-tech company Road Angel, which sells camera warning technology to drivers, said that the move should hopefully change driver habits for the better.

Gary Digva, founder, said: "I hope that deploying these vans will mean motorists will think twice before putting their foot down. Introducing these undercover mobile speed camera vans is a positive step forward in reducing the amount of speeding drivers on UK roads.

"Motorists should be aware that other police forces across the country, too, could be rolling out these covert camera vans and should watch their speed wherever they travel.

"The safest way to drive is to assume that every van you see on the road is carrying a speed camera – then you'll never break the limit, avoid fines and stay safe.

"Not only will you be slapped with a hefty fine and points on your licence, you're also seriously putting your own and other road users' lives seriously in danger."

As well as South Gloucestershire, Bradford, Great Yarmouth and Birmingham will be used as the pilot areas for the scheme. If you're heading that way, slow down – and think grey.