Sometime over the weekend something seems to have changed and now all my Apple devices can only pick up IPv6 addresses from the Smart Hub. I have tried using the "renew DHCP lease" button but that has no effect. IPv4 connectivity came back this morning but has now gone again and when the DHCP lease expires on my iPad I will be cut off again.
If you disable IPv6 ("networksetup -setv6off Wi-Fi") then you cannot connect to wifi at all, turning it back on ("networksetup -setv6automatic Wi-Fi") reconnects but again without any IPv4 connectivity.