are they plugged into the NTL master socket or another extension in the house.
Does the house have extension wiring, if so can you disconnect that and see if the master socket alone works OK.
This sounds like a missing third connection on the phone cable, Orange with white bands to pin 3
http://www.wppltd.demon.co.uk/WPP/Wi...telephone.html
This document also mentions polarity and problems with answer phones. I'd say you only have 2 pins wired though.