in the spirit of globalization, i've now added the UK to north america.
8^)
now, can anyone suggest a source for SDSL links, for private networks in the
UK?
Don't DSL links drop in maximum throughput based on cable-feet
from the CO? At 21,495,394 cable feet, your up/down speeds are
probably going to be somewhere south of 4bits/sec. 
There are a number of network operators capable of supplying SDSL (Annex B) in the UK depending on the location.
There are a chose of operators with their own DSLANs at the telephone exchanges (COs) as well as a number of wholesalers and retailers who can offer layer 2 or layer 3 access.
I'm sure there are a number of UK operators on the list (who may also contact you off-list) - can you be any more specific with your requirements?
Regards,
Really? I heard BT were phasing out SDSL due to the low take-up, and
the likes of TalkTalk are providing Annex M services with 2Mbps
upstream, capped to 2Mbps downstream, to provide SDSL-like speeds.
21CN Ethernet Access Direct circuits are probably a better choice than
SDSL, and bonding two Annex M circuits, a la Be/O2, is probably a better
choice than SDSL.
Peter