Sorry, I am probably just being thick but what do you mean "cross-connect the WAN side port to the ONT with the other cable going back up to the switch"
Use one cable going from loft to lounge to connect the WAN port to the ONT by using a short patchlead/rj45 coupler, use the second cable to connect LAN to switch in the loft.
You run one cable between the ONT and the WAN port on the BT Hub and a second cable from a LAN port on the BT hub to your switch, wherever these are located.
You run one cable between the ONT and the WAN port on the BT Hub and a second cable from a LAN port on the BT hub to your switch, wherever these are located.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local