From my experience this year Tim, just the opposite.
I have to net everything against birds. But the Brussels grew through the netting and the birds ate the tops clean off! Result? The earliest good crop of sprouts ever! Presumably, with the tops gone the plants had concentrated their energies into producing sprouts.
OK by me - I hate sprout tops, and my sister-in-law was over from Australia, so we were able to have several decent meals of sprouts, which she loves. I might do it deliberately next year.
Sorry to high-jack the thread kt: I like the web-site. It looks very thorough.