Thanks to everyone for their recommendations etc.
My current ISP does offer something that is quite new to the consumer market for bonding, but the equipment to do it is quite pricey, which isn't cost effective in the 12 month contract period.
So I'm going to go with the 2 lines / 2 network setup, which will work out better while we wait to see what happens with Openreach and the other FTTP providers in this area.
Edited by Bryer (Mon 26-Oct-20 00:41:00)