Have a look about 10pm after a rain and see if it's slugs etc. Failing that, check for sparrows during the day, becausethey sometimes do some flo damage. My money's on the gastropods
Phil J

Can you see any caterpillars on them? That's the most likely cause, I'd have thought, apart from the usual slugs. At least you have the (slight) consolation that they're almost at the end of their season of flowering. :-(

Posted at the same time, Phil!