could be, but snails live in crevices in walls too. i have one that regularly resides under the eaves of the shed.

Would caterpillars do it, Seaburn ?

Not at this time of year Louise. Possibly naughty birds but my bet is on slugs regardless of pellets.

Same here - try going out with a torch at night, and a big pair of boots on.....

Moongrower, i have caterpillars by the ton here at the mo and they're all over every single plant :(
I bought Provado at the weekend and will start treatment today.
My Heucheras are like lace doilies.

Ah you are a good deal further south than us. Though I have never yet seen a caterpillar eating a clematis.