Man of Honour
I prefer to build my own to be honest, grab a Supermicro chassis + board and then add all the other bits. Can work out cheaper than prebuilt systems.
Howcome you are going in the Docklands? The prices are ridiculous now.
No lights out management as standard, no warranty, no support. No serious business goes down that route. I've had HP come out and swap the entire chassis, motherboard, processors and RAM at 4 hours notice, thats worth paying for.
Docklands prices are proportionate to what you get, secure facilities and decent connectivity. The cheap alternative is some datacenter somebody has built on an industrial estate somewhere, maybe if you want to host a game server or something thats fine but I wouldn't touch it with a barge pole.