Potato pest eating foliage?

Is this widespread or just on one or two plants? If the caterpillars are no longer in evidence, they could have moved on to pupate. Or it could be slug damage, try looking at night or very early morning if the damage is continuing,.
If pest damage is not continuing it shouldn't affect your crop too much.
If you see a little yellow and black striped beetle on them, and orange larvae a little like ladybird larvae but larger, then report it immediately, as this would be Colorado beetle! Not likely, but as you are in Kent and the disease is endemic across the Channel it's always best to be on your guard.

Thank you.
Its on about 35% of them.
I usually dont have much trouble seeing slugs etc but I will check again at cooler times.
I have put down some slug pub traps, and oredered some nemetodes in any case . Watch this space!