I called today all set to be really narked about the fact that I've been paying £24.99 a month for 750 when the 1gig has been 17.99 for a while. Was told I'd been upgraded yesterday... Funny - my speed tests were still all 750.
Anyway after shuffling through a few people I got put through to someone who said for the set top box ones to leave STB off for at least 5 minutes as the upgrade info can take a bit longer to process, we did that and she called me back a few minutes later to confirm it all went through okay - had to reboot computer - go to
http://www.ntlworld.com to re-register my computer with the set top box (need PID and password) and then go through a box reboot and computer reboot and VOILA! speed tests came back at 2MB.
I'm in South Dorset if that helps anyone else who might be waiting in this region.