I have tried the settings/set-up you suggested and still the same. Athough I can see IPv6 enabled (and usable) on the Smart hub, I cannot get the D-Link to see it. There are a number of options for the D-link (Automatic, PPPoe etc.) on the IPv6 tab, but I don't know enough to enter the advanced settings these require to try any of them. Looking more and more like I will have to buy a DSL Modem. So anoying as the reveiws of the £20-30 ones are mixed and I can't afford to add £80 plus onto the cost of the router I incorrectly bought.
You could have a look at the IPv6 advanced settings page and see if any of the following are listed. If the D-Link supports a /56 Prefix Delegation it should work. I may be mistaken but I suspect D-Link may not properly support IPv6.
IPv6 Connectivity Native
Auto Configuration Setting Stateless
Connect to DNS Server automatically Enable
Enable Router Advertisement Enable
You will still need a proper modem for this to work as intended.