The message
from Rhiannon Macfie Miller contains these words:

Saxman wrote:
I've not grown early purple sprouting broccoli before and would
appreciate any tips
from those who have including varieties/pests etc?

Like all brassicae, it's dead easy to grow; you just need to keep away
everything else that wants to eat it before you do!

The net cage suggested by another poster is more use against pigeons
than butterflies; cabbage whites seem to have evolved a teleportation
ability! I've learnt to just pick off the eggs and caterpillars as they
appear, which isn't that onerous on a nice sunny day. Pigeons will just
use brute force (see my complaint on another thread).

It is quite possible to net against cabbage white butterflies; you
simply need a small mesh and preferably a framework which enables you to
keep the net clear of the plants. I use canes with those balls which
have holes in them.

Janet G