There are very different laws for the two sets which is why the majority tend to stick to one or the other and then only hit both either a) when they've grown enough or b) if they've got a big financial backing.
I would recommend finding someone who speaks legalese (there are members here) and having a quick chat as they'll probably know even anecdotally, a lot more than people in general. I would personally go and speak to a few already doing crowdfunding (under a guise of research) to determine why people stick to UK or USA. Failing that I'd go and speak to organisations that love startups as they will be able to tell you everything as its their business to know i.e.
3 beards, Escape The City, Startacus, Crowdcube - there are loads but they tend to have a stronger london focus. I also know of 1-2 around Bournemouth and Southampton due to family roots.