While this might sound like a good idea to some I don`t think in your situation it would be a worthy investment.
For one you don`t know the market and who you will cater your business to. For two as an affiliate only website you are at the mercy of other peoples products.
I have developed and designed a lot of websites and an online store and/or shopping mall is not easy. You can`t purchase a website and instantly start making money.
There will be endless hours of research, link exchanging, etc. How are you going to get listed on the search engines? Once they develop your site for you who has the rights to the domain name, design etc? How can you optimize the site for search engines, build link relevancy etc?
I would say keep your money in the bank and collect the interest for right now.
Do a little more research about your target market and ask questions on ownership. If the UK Company doesn’t live up to their word, what are your methods of rectifying the situation? Can you easily reach them by phone? Do they respond to emails promptly?