Is it a proper server you have? Is it going to be reliable? You do understand the implications and responsibilities you undertake in what you are doing? (IE if the PSU dies on christmas morning it is you who is going to be finding the spares and getting them to the DC, and then some charge for access or need 24 hours notice).
As Alex mentioned have you checked out your power usage? Power is expensive so if you have a power hungry device it will be expensive.
You need to consider if you need it in the Docklands, London, close to London, other locations such as Manchester or Leeds.
All of this will affect your decision on the host for you.
Alternatively have you thought about using something like a virtual server? If you pick a decent provider you can get a very powerful and fast server for not a lot of money which (if properly set up) can handle some serious traffic. Ill give you a recent example, I had a customer hit heavy with visitors for their event due to snow. They were getting over a hundred requests every second at some points in the day. This was dealt with using just 20 MB or ram (the server had 128MB). They shifted 120GB of data in 3 days and the page was just text and a couple of small images for the design!