Nick,
one of the issues highlighted by 'our' HSE visit was the need to secure the main egress, which, like Smallcleugh, is stone arched. There were major areas of spalling due to pressure cracks, missing stones, and an interesting run of missing blocks at shin height, which we deduced were probably caused by ice on top of the standing water, in the winters of 45 and 63.
Dr KW suggested that replacing all missing stones and mortar pointing the worst areas would even out the stresses across the arching. The 'point' of the pointing is not to glue things in place, but to act as lots of little keystones, thereby allowing the downward forces to be spread more evenly.
Job now done, and Colins concreting is a wonder to behold!
Nice job for summer or autumn!
MARK