Does anyone know what's eating my pak choi?

[Antaresisastar]

The leaves are full of holes, is there anything I can do or should I just pull them up?

Flea Beetle, I have them too and difficult to get rid of. Sometimes if you leave the plant alone the middle leaves are not touched by them and look ok. Leaves are still ok to eat but maje sure you wash them in salty water.
Here is what the RHS say
www.rhs.org.uk/advice/profile?PID=510

Thank you Farsley Lass, will wait and watch for a while.

It's so annoying. Rendering useless all my come again leaves and rocket. However the lettuces that were planted as rather large seedlings are fine. Do they also usually attack lettuces?

Hiahia, they also attacked my radishes, but not until the bulbs had swelled, so they were edible, no sign of their damage on the lettuce or the Chard. My pak choi was planted as seedlings, the seedlings were outside for ages and weren't nibbled.
This is my first year of growing veg, so I expected it to be a learning curve, the words "brassica cage" gave me the chills, but perhaps now I know why these things need protecting! Will a v fine mesh cage keep these buggers out though? Perhaps someone with a lot more experience can advise?

As i understand it flea beetle live in the soil and are really annoying as mesh does not keep them off. They attack brassica so lettuce are not attacked. I find they only attack pak choi and radish my cabbages they leave alone. With radish they eat the leaves but not the bulbs which is good news as I really enjoy radish.