Do you want to run servers directly of a local LAN? If so there are many leased line providers available in the UK. Usually these are the large Telco's like a BT, Cable and Wireless, etc.
Many ISP's UUNET/MCI, Cable and Wireless and Tiscali will sell leased lines, but will have to get this through BT anyway. But they do get discounted rates because they are buying in bulk. Cost is really affected by the size of the leased line you want.
You can get E1 (2meg) aggregated into 64kb sections. So the smallest you can get is 64k. The nice thing about BT is they will deliver 64k bandwidth on an E1 and then you can easily upgrade your line in 64K sections. You pay for the line rental of E1 but only the bandwidth of 64K.
If you are not running these server on your local LAN, then Co-location is the best option. This give you support, redundancy and backup solution in a nutshell.
A company called Band-X,
http://www.band-x.com/en/, provides an innovative service for capacity. I wont go through the whole thing, but check out their website and have a read.