AN EXPERIENCED caver was crushed to death when a shard of rock fell on him as he crawled through a narrow passageway deep underground, an inquest heard.

Gordon Aitken, who worked at Kendal-based South Lakes Housing, was killed when the slab of limestone, said to weigh three to four tons, became dislodged in a freak accident beneath the Yorkshire Dales.

But the reason for the rockfall in the 80-metre deep Bull Pot cave, near Ingleton, remained a mystery, said coroner Rob Turnbull.

Yorkshire Subterranean Society member Shahrzad Mohamadi, of Leeds, described to the Skipton inquest how she heard the sound of 50-year-old Mr Aitken, a fellow society member, crawling on pebbles just before a loud thud.

They had completed three pitches down the cave on February 14 and Mr Aitken, who lived in Lancaster but had worked at South Lakes Housing for 25 years, had gone to explore a passage.

"I had stopped to take a drink when I heard a noise - like something huge had fallen. I shouted: 'Gordon, are you OK' but I heard nothing. I knew something terrible had happened," said Miss Mohamadi.

"I entered the passage where I had to stoop low and saw him on the floor with a rock on top of him. I checked if he was breathing, but he wasn't."

Martin Colledge, of the Clapham-based Cave Rescue Organisation, said when he entered the passageway he saw Mr Aitken with his back to him, kneeling on one leg and with the other stretched out behind.

"His back was sloping away and there was a large flake of rock on his back and head," said Mr Colledge.

It was too heavy to lift, so the rock was broken up and removed in pieces before Mr Aitken was stretchered out of the cave where he was pronounced dead by a doctor at the cave entrance.

Mr Turnbull, who recorded a verdict that Mr Aitken had died as a result of an accident, confirmed there had been a minor earth tremor in recent days before the accident but an expert at the British Geological Society believed it was too small to have dislodged the rock.

Bull Pot - a Grade 3 pot hole in terms of difficulty - is part of a huge cave system which links Yorkshire, Lancashire and Cumbria.