Unprotected brassicas

I don't know Tsoi Sim but your collection of pests is typical of those affecting the most common brassicas like cabbage and cauliflower.

Some plants don't look much like typical brassicas but nevertheless are; rocket and radish are two which possibly don't suffer quite as much although seeing either of those without flea-beetle damage is rare in my experience. 

JayG, I had some rocket next to it that did great until the tsoi sim started to grow, then they both got invaded by the pests. I'll stick to grow under cover, my cabbages and broccoli under net are picture perfect.
I have harvested what I could of the tsoi sim (it tasted really delicious, both the leaves and the long flower stems), and pulled out all the rocket. Sigh.
madcat, I'll try what you suggest! I might pull out some of the slower growing plants to make room for these. They were ready to eat in 4 weeks, and keep producing after you cut the first harvest, and they were really good so I'm not sure that seen my very limited space I should keep things like cauliflowers that take 4 times as long.
If you have problems with pigeons, can I suggest you a mad experiment against pigeons? I was worried about the woodpigeons that nest a few yards from my raised beds. I read on a US forum that fake snakes spook birds; they don't have to be realistic, so I just put a couple of garish plastic ones next to the plants I wanted to protect, and none has been touched by birds. I'd love for more people to try this to see if it's a coincidence or if it really works.

Thanks for the suggestion, I thought about it but I have tomatoes on one side of the bed, growing against a tall trellis, and some tall peas on another side of the bed. Basically, there is no easy way to get a net on only part of the raised bed (since I use square foot gardening, there is a grid on the bed that it's very good for a lot of other things but it makes hard to net part of the bed). I'll get the hubby to take a look and see if he can come up with one of his usual brilliant ideas...