There's a rough estimate that 500,000 people in the UK keep chickens, out of a 60,000,000 population. This is mostly due to townies getting eglus and coming over all 'Good Life'-ish. There's a lovely little family-run pet shop in the poshest area of town that sells chick starter, grower and layer, organic and non-organic. I asked him how much of it he manages to shift and he reeled off a list of about 15 people nearby who came in for the stuff.
If you'd asked me 5 years ago if I thought I'd end up with chickens, I'd have rubbished it, but now, well, I can't see my life without chickens.
Edit: the gov. department of agriculture, DEFRA (or as I like to call them, DEATHRA), really has no idea that so many people keep chickens in the city. There was a short article in Practical Poultry about the fact that someone had invited DEFRA officials to her home to see how she kept her 6 orps, and they were amazed that chickens came in a colour other than brown or white, and that anyone kept them as pets. DEFRA have a well deserved reputation for not knowing what's happening on the ground, and ever since they screwed up their handling of Foot and Mouth Disease back in 2001, nobody trusts them any further than they can through them.