IT could have been a frustrated motorist or, possibly, a student prank.

Police are refusing to speculate on the culprits, but someone has helped themselves to more than 1,000 motorway traffic cones.

Detectives say they are treating the theft of the cones - from a three mile stretch of the A1(M) between Newton Aycliffe, County Durham, and the A68 Burtree Interchange - "as a serious matter".

The cones, which are worth up to £7 each, were to be used to block off lanes on the motorway while a highways contractor carried out bridge-strengthening work.

After being left on Saturday afternoon, workers returned at 6am on Monday to find they had gone.

Detective Sergeant Alec Francis, of Darlington Police, said 1,100 cones had been taken from the hard shoulder on both sides of the carriageway.

He said: "We have made inquiries with motorway contractors in the area and the council depots but there is no sign of them.

"You are taking about £7,000 worth of property and it would take a couple of hours and a van to shift them.

"It would, however, be quite natural to see someone loading cones on a vehicle at all times of night as they are used for motorway repair."

A spokesman for Durham Police said they had never witnessed a theft of cones on such a scale. "It is very unusual and it might seem like a prank to many people, but we regard it as a serious matter," he said.

"The work on the motorway has been delayed and real inconvenience caused to the contractors."

Anyone who saw the theft should call police on (01325) 467681 or Crimestoppers on (0800) 555111.