There are loads of arcades in London, the likes of Marex, Elite, Saxon, STA etc.....basically it is a company that provides the facility to set up a group of traders, provide them with news, charting, software, clearing, coaching (if needed) in exchange a trader will do one of 2 things.
1) deposit funds with them in order to be given size to trade and pay a monthly desk cost plus brokerage per lot.
2) deposit little or no funds, be given size to trade, paying desk costs, plus brokerage and a percentage of profits.
Refco Trading Services, prior to going bust due to the run on the company offered this service in London, Gibraltar, Chicago, New York and Montreal. The US offices were taken on by MAN in the UK by MAREX and Montreal went there own way i believe. I don't believe any of the others operate this side of the Atlantic.
At one stage Refco in London had 200 plus traders, now Marex London is about 60 plus. STA (Schneider Trading Associates) is probably 80 plus. Saxon and Elite i have no idea. There are others aswell. Some of these offer remote trading aswell, via either VPN or dedicated lines.
If you do google those names in the co.uk sections you will get more info.
Chris