I have the same problem as well.
Phoned NTL they blamed my router then zone alarm
Connected direct into modem with no zone alarm still the same.
They say it cant be the modem (120) as its able to handle the new 10 meg
speeds.I never had any problem on 3 meg now its utter crap
NTL seem very reluctant to admit they have a problem with the older modems but from the number of complaints on this and other forums they obiously do.So come on NTL admit it and do something about it instead of fobbing us off.