I use BT openreach too. They do but as I said patchy connectivity. I see that when I run nslookup in windows which isn't smart enough to fall back to IPv4 DNS when v6 is not reachable. It seems to be on and off.
https://www.aa.net.uk/ https://www.aa.net.uk/ I'm using it and get rock solid IPv6. Also they have actual people who know what they are doing manning the phones.