Thanks Alan, yes I do get masses of tubers. I tried to dig a lot more out last year and gave bagfuls to both Piglet and Tigger. However, despite us digging up every artichoke in sight, the patch is more dense than ever.

It's a good job I like them; I'd never tried them before I inherited this lot.
I've decided I'm going to try graduated pruning and see what difference it makes. I'll start at 3ft at one end and go up to full height at the other. I'll have enough tubers whatever I do.
I'll let you all know the result.
Thanks again everyone.