If they do this by issuing real IPv6 addresses, with CGNAT to IPv4, I actually don't have a problem with it. but using it in full IPv4 mode just makes the existing situation worse.
I don't disagree with that at all. I wish I knew what BT's plans were in this instance, but at some point CGNAT will need to be rolled out. I guess you could argue that IPv6 is less of a priority because if IPv4 addresses run out, people are screwed and ISP's need to have a solution in place - right now, IPv6 is not that solution because it only gets you on to the (rather small and limited) IPv6 internet.