Your DNS requests (port 53) are being intercepted by either BT Protect, or BT Parental controls. Parental controls may have been activated by BT automatically, similar to what othe ISPs are doing. They are usually set to "light".
If you go into MyBT, you can check this.
It does not always show this, so to make sure, enable parental controls first. That will then give you the option to totally delete them.
Then reboot the home hub, and flush any DNS caches.