I’d like to use the aggregated WAN load balancing but just need some guidance.

The property is cat 5 wired throughout but where the BT wires come into the property, these are at different ends.

Do I just plug both routers into the LAN or do I have to physically connect both routers with a patch lead?

Gives us a bit more... do you have two BT circuits? What type are they/is it? Do you have a central switch?

So yes, there are two BT lines which come into the building and they are both FTTC enabled. The property is Cat 5 wired and there is a central un-managed switch.

OK great. So what devices do you have?

Basically you need two FTTC modems obviously but one could be an integrated modem in a router.

E.g. could use 1x 166 modem and 1x 2865 router, or 2x 166 modem and 1x 2927 router.

You want the FTTC devices as close to the BT master sockets as you can. Then cable to 166(s) to the router. If you use a 2865 you will have 1x VDSL directly connected and the 166 connected to WAN2 port over cat5.

If you use a 2927, you will have both 166 modems cabled to the router over cat5 and the router can be anywhere.

Thanks for the assistance so far with this.

I have a 2860 and a 2862.

In terms of connecting the two routers together, can they be connected together via the LAN so the data flows through the network switch or must the two routers be connected directly together with a patch lead and not go through the router?

In this scenario, the 2862 will be your router (since it's newer and faster) and the 2860 would be configured for PPPoE pass-through per this article , basically turning into a 166 modem.

Line 1 -> 2862 DSL port
Line 2 -> 2860 DSL port
2860 LAN1 -> 2862 WAN2

ISP connection info (i.e. username/passwords) will be configured on the 2862, with the primary line as WAN1 and the secondary connection as WAN2. Be sure to set the MTUs accordingly everywhere, most likely you can use 1500 across the board. Then set the load balance/failover policy on the 2862 as appropriate.