@AtaxyaNetwork
Thanks, I'd come to this conclusion after posting. I must have done this when I was using a free trial as it was all working until the weekend when we updated hardware and now have new pools - so he can't see the new pools (and the old pools have gone). I did find an error in the logs about permissions, so this all ties up.
Followup question: Do you have Xen Orchestra just running as a VM in the pool or on it's own server ?
Reason: Due to CPU hardware differences, I wasn't able to do a live migration between our old servers and new. This meant shutting down each VM, moving and then starting up again. I obviously couldn't do this with the VM running Xen Orchestra and used XCP-ng Centre app (confession, I ended up doing ~90% of moves via the app. I'd tried using Xen Orchestra but the extra clicks involved alone made an already laborious task more so).