Thank you to everyone for your responses. I'm now much more confident that I am able to move away from my current ISP with minimal disruption.

I had seen the PPPoE setting but never understood what it is until now - always learning!

A couple of you were mentioning my setup - we're in a suburban part of W London and while the AX11000 would ordinarily be a little overkill, our property is split over four floors with several blackspots caused by the building materials. I took the chance to hard wire everything we could along with the two routers at opposite ends of the house back in 2019. When it came to working from home, I found the setup handled the additional strain without complaint. Highly recommended to anyone looking to do something similar - the AiMesh function with Ethernet backhaul is very easy to set up.

Thanks to everyone again for the advice.

I had cause to use one of those AX11000s recently in a harsh RF environment - it performed well.