From what I know (and I could be wrong), but BT have enabled v6 on their consumer infinity connections but not their business infinity connections. Which is rather annoying.
I've got v6 working the same way i've had a few years now, via a 6in4 tunnel to my Hurricane Electric (tunnelbroker) account.
Every now and then I turn that off and try to get my router to get a native v6 connection from BT in the hope they've turned it on, but as yet, no joy...