I noticed on my bill that NTL had upgraded my service from 1Mb/s to 2Mb/s. I still measured 1Mb/s.
I complained to NTL. They emailed me a list of standard things to try which had no effect. I complained again but they assured me that the 2Mb/s configuration had been done and the problem was mine. Three days later my service was miraculously working at 2Mb/s.
Mine will only go up to 1mb maximum. NTL told me they would have to replace the box with a later one. I didn't want all that messing around so I opted for a standalone Modem. The engineer arrived a couple of days later and installed the modem and now I am upgraded to 4mb for the same monthly fee, £24.99.