In reply to ClimbingNut:
Fun question! I suspect it depends how you count it, if we're talking 'number of distinct routes' I suspect lowland crags probably take it just because there's so much stuff recorded in areas like the peak and yorkshire. If we're talking meters of climbing then it might swing towards the mountain crags. I'd be surprised if there's enough sea cliffs to make the cut, though I think they're outsized in terms of quality.
To try and inject some #science I did a quick count of all the guidebooks on my shelf (96 unique volumes, latest coverage of an area only, decent coverage of the UK but with some big gaps in scotland). Of those I'd classify 51 as covering 'lowland crags', so assuming there's a broadly even distribution of climbs in guidebooks that's (very approximately) 55% of the climbing in the UK.
