Hi Chris

The nice thing about growing broccoli is that the problems have all
disappeared by the time you're eating it. So you don't have to spray at
all.
I let the caterpillars eat most of the leaves and it doesn't seem to
matter.
The plants still survive. Have others found this?

Yes - same situation here.
Caterpillars happily munching on the leaves of the purple sprouting -
but, by the time we come to eat the sprouts the pests will be long gone.

I showed the caterpillars to the bantams - but they didn't seem interested!

Gave some purple sprouting plants to a neighbour last year - cropped well - asked
this year if they's like some more. Answer "No thanks - my husband got too
stressed trying to keep the caterpillars off them".

Odd ideas some people have about gardening, don't they?

Regards
Adrian
Suffolk UK