They were in a Ford Transit drop-sided van which was stolen between 12.35pm and 12.45pm on Thursday 16 February 2012, from Lunnfields Lane near Burton Salmon. The stolen Transit is white cab and black body. Its registration number is NA11ONR.

In the cab of the Transit were two bags containing 16 foghorn detonators for use on railway lines. They are yellow, approximately 5cm in diameter and attached to two lead straps.

PC Dave Clark, of Selby Safer Neighbourhood Team said, "We do not believe that the thieves knew the detonators were in the vehicle at the time and may have since dumped them somewhere.

"The stolen detonators do not pose a risk if they are handled correctly. However, despite their small size, if they are misused they may cause a serious injury.

"The detonators have no use other than alerting train drivers of potential hazards on the track.

"I urge anyone who may have seen the detonators, since the theft, to contact the North Yorkshire Police or Crimestoppers immediately."

Anyone who can help the police with their enquiries is asked to contact Selby police on 101. Press option 2 and ask for David Clark.

Or call Crimestoppers anonymously on 0800 555 111 quoting reference number 12120024710.