I also go for snails.. it's a very typical snalis damage... if you see in the picture, you can see that part of the leaf around the "bite" is lighter, which suggested that on the other side, the lead has been eaten too, but not complete...
Debs, if you want to check for snails in your pots, a good trick is to put some cucumber slices on top of them, just after watering and leaving them overnight. Next day, early morning, just pic the slices, if you have snails living there, you will have them eating from the cucumber... repeat it for a few days, if you do not find any the first 2 or 3 days
Snails can be quite small, and sometimes difficult to see in the pots, without this kind of tricks (my own experience
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