Thanks to everyone regarding the problem. I think it must be caterpillar,
no signs of slugs anywhere.
They prefer the more showy ones with large flowers, not the self sown ones
unfortunately.

Ann

After I'd replied to you, I thought about the damage and thought it sounded more like caterpillars. Slugs either go for stems, so that you get wilting branches, or the entire plant is felled, or they make holes in leaves (like hostas). Disappearance of entire leaves is much more like caterpillar damage. But I don't know which caterpillar favours aquilegia ((they're very specific). Is there an aquilegia sawfly? - ah, yes there is:

The Aquilegia sawfly,iPristophora aquilegiae/i

kay wrote:
After I'd replied to you, I thought about the damage and thought it
sounded more like caterpillars. Slugs either go for stems, so that you
get wilting branches, or the entire plant is felled, or they make holes
in leaves (like hostas). Disappearance of entire leaves is much more
like caterpillar damage.

Oh, I don't know, I think my dahlias will happily* contest that whole leaf
removal isn't beyond the little buggers. :-(