And just realised why mine works - it's provisioned through Openreach and not CityFibre so no VLAN required (and to be fair the setup guide does say it's only CityFibre that requires a VLAN).

Thanks @el_Gordo - I wouldn't have thought to look under LAN/IPTV to find it!

Weirdly though I've not needed it on my RT-AX86U Pro to connect to Aquiss - it works without setting up VLANs.

Hi, Not sure if you're still having a problem with connecting your RT-AX86U Pro to Aquiss? If so then shout as I've the same router running Merlin connected OK to Aquiss without VLAN tagging (it's not an option in the Merlin firmware). It did take a bit of fiddling but it's up and working fine on IP...