Yep, it's true. According to Oftel (or Ofcom as I think they are now) NTL, BT, Pipex and Tiscali were the most complained about ISPs.
NTL was better than One-Tel, but both were merely average and AOL & Freeserve are the best...
Have a look at
http://news.bbc.co.uk/1/hi/business/3284529.stm