"Scotland has more known vitrified forts than anywhere else in Europe and here in Stirling we have our own that reflects our warlike past, " he said.

BBC: Archaeologists probe Abbey Craig secrets

Archaeologists first discovered the 1, 300-year-old fort 10 years ago and concluded it was engulfed by a ferocious fire that fused together - or vitrified - the stone walls during a siege.

BBC: Archaeologists probe Abbey Craig secrets

David Sanderson, a physicist at the Scottish universities' research and reactor centre, says that while this would need heavy investment (and a lot of workers), plutonium can be mixed with waste and vitrified into storable glass blocks, so making it unusable in bombs if any terrorists managed to steal some.

ECONOMIST: The nuclear industry