Big improvement today when using automatically-assigned proxies. Still not brilliant, but not bad.
ntl responded to an email complaint I sent a few days ago too:
We are sorry you have been experiencing problems with this facility. There is some work being done at present to upgrade our network capacity. Unfortunately, while this work is going on there will be unavoidable degradation to some aspects of the service. We are making every effort to minimise the impact of this, and I can assure you we will restore to normal service as soon as possible.
I guess this is standard stuff, but at least they acknowledge there's a problem.