Can I use a VLAN?

[devnull]

Try this VLAN configuration and see if it works when you get the new router.
Switch A, Port 2 => modem, configured as VLAN 2 tagged
Switch A, Port 1 => Switch B, Port 1, configured as trunk
Switch A, Port 3-8 => clients, VLAN 4 tagged

Switch B, Port 1 => Switch A, Port 1, trunk
Switch B, Port 2 => Router WAN Port, configured as VLAN 2 tagged
Switch B, Port 3 => Router LAN Port, configured as VLAN 4 tagged
Switch B, Port 4-8 => clients, VLAN 4 tagged

Note that you should connect the router directly to the modem first, since you will need to make certain that the internet connection works before you run this setup.

[Kiangs]

Thanks again, will try that when I get the new router (hopefully by the weekend...)

Good idea with the ethernet splitter but unfortunately it won't really help in my particular circumstances. As long as I can get the VLAN shenanigans sorted though it'll do fine for now. Fingers crossed!