I'm in the UK - Derby, specifically, though I've known other areas well too - and I've never seen people working for more than a short period (say, 30 mins max) out of cafés. Never.
I can see it may well be good networking advice. I can see it'd be more sociable than my current spare-bedroom-office setup. But I've never seen it done to have any indication it's viable in the local café culture.
Serious question. Any UK'ers, midlands in particular, actually do this? Where do you find is actually good for this?