Somerset, United Kingdom

I'm not sure whether my last attempt to post a question actually worked, so here goes again:
Some of my winter and spring cabbages and all of my sprouts are afflicted with a wierd condition which I can't find in any of my books: hard white nodules, ranging from quite small to 2 or more inches across have appeard on the leaves. The sprout plants are stunted (some no more than a foot high), while many have strange hard, white, largish hook-like lumps where the developing sprout should be. I'm thinking maybe some kind of fungal thing perhaps. Any ideas?

• 10 Sep, 2014