Hi Biscuitfuelled, many years ago in my diving days we used to traipse over to Hodge Close Quarry in Cumbria. I know its not Scotland but it was an eminently suitable training venue for both open-water and cave diving.
FWIW, in 1986 Steve Kemp & I assisted by 2 other 'sherpas' from York Uni SAC dived the Sir Francis engine shaft - hand over hand down the winding cable to 30m then straight back up. Could see absolutely ******-all! Didn't even consider going along the drift at the bottom, we'd be in there yet.
For those who are wondering, we considered it an 'Open water dive with restricted access' rather than a 'Cave Dive' per se.
never again, mind ::)
MARK