I just checked and it says they moved their operations to the UK, but every time I ring I get diverted to an international ring tone, all their staff names are foreign (which doesn't mean much I suspect thats the case with most of London admittedly) and they appear to operate on GMT+1 time, also the only address they give is a forwarding address.
I don't think any bitstamp employees are actually IN the UK, despite what they may claim.
The company is incorporated in Reading, Berkshire. They probably don't have any staff there, but they're still operating under British law. I suppose that they moved the legal registration in the UK for tax purposes and because they anticipated that Bitcoin regulation would be lighter compared to whatever might happen in the Euro area as soon as the authorities decide how to act.