Thanks very much to both of you! Sorry for the late reply. My phone was stolen and I've been a bit preoccupied as a result!
I'll search the plants closely to see if I can mind spider mites or mealy bug - I think I definitely had the latter on my parsley, which I ended up throwing away, at least the leaves got a film of fuzz and lots of white spots... And that was growing in the same place. But I haven't seen any fuzz on the leaves of the tomatoes/peppers, just white spots that grow larger and have black spots in them, but look similar to what the parsley had.
The plants are indeed inside but I thought they'd be ok as it's a conservatory and probably about as sunny as my garden... but could the glass be causing them to burn? I try to water them everyday and feed tomato food weekly, but haven't been religious about the latter.
They are almost all very skinny and not the best raised plants - it's my first time and I let them grow too tall in too small pots. I'm still trying to stem their growth by snipping the top off and removing new shoots that appear, but I guess this year will be more of a lesson on what not to do.
I just noticed that the plant you point to as probably sunburnt, Pat (pic #5), has bugs on it that look like small beetles - they're fairly big, about 3-4 mm across with a green body and black head with the black running out onto the back like a small cape, another two black spots down the middle of the back and black legs. I'm looking for pictures to match online but haven't had any luck yet. I haven't noticed these before on any of the plants, but just now I found a few of them.
Thanks again for your advice!
Olof