I think I've got it all working. Moved the old 585 router from 192.168.1.254 to 192.168.1.253 and turned off its DHCP. Turned off wifi on the new router. Plugged everything up so that the new router is only acting as a bridge from the WAN port to one of its LAN ports. The old 585 is doing all the rest of the work.
As I understand it, the new router is doing DHCP and NAT. The 585 is doing wifi. What's specifiying DNS? Probably the new router but not sure that I care.
Lovely mess in my hall cupboard where all this stuff lives. Perhaps I should buy myself a high quality integrated VDSL modem/router and just have one box. Any suggestions?
PS: Have also raised ticket with PN. They'll probably swap the router but I have a feeling that the new one won't be any better. That's why I'm considering buying a decent modem/router.
Edited by ppppenguin99 (Sun 19-Apr-15 19:43:02)