It's in the UK on paper and that's all. Every name I've heard associated with it is Slovenian.

From the wikipedia page - 'The company is registered in Reading in the UK, but this is in fact just the offices of UK PLC, a company specialising in company formation and which, amongst its services, allows companies to use its own address as their registered office, effectively acting as a forwarding address. There is no clear information available as to where Bitstamp's operations are located or whether they actually have any presence at all in the UK, or are still run out of Slovenia.'