Tiny caterpillars would be my main suspects. I have already removed a few butterflies from my greenhouse. Have a regular look under the leaves.

I agree with Jimmy, looks like snails or caterpillars of some sort. You can pick up any of the organic nontoxic iron phosphate baits, such as Sluggo. That's what I use on my cabbage and hostas and seems to work.

slugs/snails or even woodlice.

Thank you for your replies.