Ummm. If you see them at night, they're not flea beetles.

Please describe them (size; color; where they are [top or underside of leaf]; how they move) and tell us what sort of damage you see.

Better yet is a good photo.

Hi and thanks.
they are very small.I would say 2 or 3 times the size of a grain of sugar.I had to put my glasses on to see detail.
Its about 4 legs each side and small wings.The colour is grey/brown.They have worked the leaves down to stumps but I don't think they go under the leaves although they seem to findout of the way parts of the plant.
They are quite easy to catch and I carried one back up to the kitchen on the palm of my hand but they do tend to jump off and you then see them moving quite quickly on the soil under the plant -ie walking or running.
I don't think they attack the stem of the plant at first but it looks as though when the leaf is finished they carry on with what is left.I did think it was the slugs doing the damage but have more or less discounted that as I have replacement plants growing in a protected area that have been damaged the same way as the plants that I sowed directly into the ground.
I have tried to photograph them but I don't know how it will turn out as I don't have a digital camera and it will take a few days to get developed.
I am fairly sure that if I cover them with fleece (remay) it will solve the problem but I was hoping the plants would grow through it .But the pests seem to be setting them back a lot and some may have died even though they can come back from very little left.
My suspicion is that they may be young weevils of some kind as they have a hard shell but they are thinner than the ordinary weevils I sometimes see and I am sure they have wings (the ones I had noticed before)