I think by "after BT's 21CN upgrade" Roger probably meant that his exchange had been switched to 21CN. He lives fairly centrally in London, so it seems likely.

While 21CN doesn't automatically mean higher speeds, when it is announced that your exchange had been upgraded to 21CN then that also means ADSL2+ DSLAMs for your exchange. Or at least that is my understanding after following what Adrian for AAISP has been saying for the last year or so and he normally knows more about what BT are doing with ADSL than they do...

I've still got another year to wait for my exchange to switch.