All depends on what speed site test you are using. Use the one from this site, gives a better reading.
Sometimes it's just a case of something out on the system having a paddy and you needing to reboot modem/router to get things back in line.
No worries, if I can stop the calls to the *coughs* help line by offering a little advice here, then it's all good as far as I am concerned. It also shows there are still people that work for NTL that take pride in their job