As regards the netting, I found, on the Internet a company called
Haxnicks, which produces a fine netting called "EcoGreenMicromesh". It
seems to be made of nylon rather than plastic (though they don't seem
to say) and should, so they say, last for ten years, if looked after.
It's very reasonably priced for the size of the sheet and is fine
enough to keep out, so they again say, cabbage root fly, carrot fly,
white fly, onion fly, flea beetle, vine weevil, aphids, bees, wasps,
cutworm and other caterpillars, moths and butterflies, and others. It
will also keep the birds off.

I've only used it on my carrots, so far, but I've had no problem with
them this year.
.
Hope this helps!

John


An alternative (and in my case, cheaper) netting material is that used
by scaffolding firms to protect the public below from falling masonry
etc. They all use it, they have to !
They call it Debris Netting or Safety Barrier Netting or something like
that. Such firms often have some to give away, or sell-off cheaply.
Even if slightly torn it is easily repaired with some wire-ties or even
with a bit of sewing.
Worth a few calls to local firms.

p. pleater