Lots of people reporting here that online upgrading does not seem to work for them, well it did for me when I visited:
http://www.ntlworld.com/data-feeds/editorial/microsites/tierMigration/
It took about five minutes and no reboot needed.
One of the few times that I have been happy with NTL!!!
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Oh, addition to the above. I live in Oxford. Maybe the region is important