@ Harrison
Noise Margin is not something they can just set.
The noise margin is a resultant figure based on length of copper wire, quality of paired wires & the speed applied to it. No matter how your ISP explain it to you, they just can't pull a Noise Margin out of the air & throw it on your phone line.
I would ask them to reduce the upstream speed, which should throw some more db back at the downstream noise margin. Slowing the downtream speed would also help increase the noise margin too. Personally, I would say your service is a bit top heavy with an upstream speed of almost 1Mb & would suggest a 768k-ish upstream speed for a better overall experience. If you get very little increase in D/S noise margin, ask them to reduce the D/S speed as well. That should help your high 54db Line Attenuation. The higher the Attenuation, the slower your speeds need to be.
Just for the crack, open a DOS prompt & type:
ping w.w.w.ukonline.co.uk -t (no dots in the www of course)
Grab a screenie if you see spikes.
Also, did you manage to trace your route to the exchange and calculate your distance?