I have also experienced a fall-off in speed over the last 2 moinths. My Breeze Light is giving me less than 56K at present even though it is supposed to be 2M. I have sent emails which are unanswered and spent hours on-hold carrying out tests which Surprise surprise! showed that I was getting erratic speeds from 18K -70K.
NTL are offering 3 M for the same price - guess where I am going!