CCTV cameras that are normally used to monitor traffic flow at the Green Road 'hamburger' roundabout are being used to catch a mystery traffic light tamperer.

Twice this month someone with a special tool - used only by highways engineers - has opened the control box to switch off the lights at the redesigned roundabout in Headington.

Following the latest act of vandalism on Sunday night, engineers have altered the direction of the CCTV camera so that it faces the signal control box in an attempt to catch the culprit.

Principal engineer Colin Baird said: "The CCTV will now be used to watch the signal control box as well as the traffic. We can only assume the motives were mischievous.

"It was certainly an irresponsible act and tiresome in the extreme for the county council and road users.

"It must have been carried out by someone who knows what they are doing and who has access to a special tool to open the control box.

"They opened it in such a way so as to make it not obvious it was done when the door was opened."

County councillor David Robertson, cabinet member for transport, rejected the suggestion that it might be someone protesting about the new road layout.

He said: "I can't imagine it would be somebody going to do it on purpose because they preferred the roundabout before the lights were installed.

"Everywhere I go people say how fantastic the new system is and how much better it is than before the road improvement measures took place.

"It is unfortunate that someone felt so self-important they sought to cause chaos and disruption to so many people."