Might be Tomato Moth Caterpillar - the larvae, or caterpillars, range in colour from pale green, pale brown through to brown, and yes, they do feed in the evenings. Ultraviolet light shone on them at night reveals them more clearly, because they fluoresce a bit, but failing that, a torch at dusk and a pair of stout shoes for squishing. Pupates in the soil over winter, so if you're growing in a greenhouse in soil, dig over thoroughly when the crop's finished and add some fine mesh to the doorway to try to stop the adult moths flying in to lay eggs. I think there's a pheremone trap for these, but not sure.

Thanks Bamboo. It's very disheartening this year: there seems to be pest for just about everything! And the snails.....never seen anything like it!

I try not to think about the fact that we have, in the last 4 years, acquired many new pests and diseases which affect plants, it's too depressing, because most of them are difficult or impossible to treat - although I think tomato moth has been around a while.