Its seems the Nokia Lumia 710 is a pretty good mover, as it is completely sold out on Orange UK. The cyan Nokia Lumia 800 is similarly affected, though the black version is still available.
Interestingly the Nokia Lumia 800 on Orange UK does not have a great overall review score, achieving only 7.9/10, with the handset mainly let down by poor battery life. Hopefully the various firmware updates Nokia has already released to address the issue will go some way to repair this issue.
Thanks Alex for the tip.