The City of London is a bit like how in Robocop II where OCP forecloses on Detroit and takes over the running of a city, including the police. It is an area of London run by corporations, for corporations. There is a directive 4 just as in Robocop, which is why there are virtually no prosecutions of bankers and other financiers in London.

Arrest warrrants are basically a thing of the past in the UK - the police rarely need or use them. I imagine the proxy server owner was arrested for conspiracy to commit copyright infringment or conspiracy to commit fraud.