Soldato
Thanks for that.I've found that you don't need the DHCP Option 61 on my FTTP connection, just setup DHCPv6 and it sprang into life, authenticates and run very quickly. You could use another Express or the U6 Mesh. I've got a u6 mesh stuck on top of a unit in the kitchen and that works really well and comes with a POE injector in the box.
Just to double check, are you with Sky (FTTP)?
Everything i've read seems to point to 'Option 61' needing to be enabled for FTTP (*DSL required username/password + PPPoE i believe) but if not then that's worth noting.
Will look at the U6
The only reason i liked the idea of the AC Mesh Pro is that it's bottom fed and i could mount it next to one of the network sockets in the office rather than opting for the other in-walls that, whilst it would look neater, i would need to cut a section in the wall and relocate one of the cat5e runs and i'm not sure there's much movement in the run to do that - they were done by the developer and they're a mess although work at 1Gb.