I used to have a old VR400 which not worked with IPv6, but i got them a beta firmware which worked. So i guess maybe VR900 also have the same beta firmware.
Just email them and ask for this.

alec_alec wrote

I used to have a old VR400 which not worked with IPv6, but i got them a beta firmware which worked. So i guess maybe VR900 also have the same beta firmware.
Just email them and ask for this.

Email who? tp-link?

Of course tplink support. I think uk.tp-link.com should have their mail address

As previous post email/online chat with TP-Link to request beta firmware for BT IPv6 compatibility.
Once firmware has been updated the router login will change to http://192.168.1.1 not http://tplinkmodem.net
Use the following configuration settings (I used these on VR900v1 to get IPV6 to work):-

BT DNS servers are:-
Primary: 81.139.57.100
Secondary: 81.139.56.100

Advanced/Network/Internet
Modify/Edit connection
Enable IPV6
Address type: DHCPv6
IPV6 gateway: Current connection
OK
Advanced/Network/LAN Settings
IPV6
RADVD
Delegated
Save

I hope this helps?