I think I might contact some PHP developers and see how hard it is to create a currency exchange website. I literally cannot understand why no one has created a UK version of those websites yet.
You are thinking bottom up instead of top down. Exchanges / exchange ideas fail in the UK because no banks want to deal with you. Don't waste your money on programming anything unless you have knowledge of all the paperwork you would have to do for each customer / transaction, that's if you could ever get a bank account in the first place. The UK is even more regulated than US / many places in Europe, hence no exchange. Nothing to do with PHP.