I'm not sure about the other lounge in LGW, but I know that the P-club in LGW is located outside of security. If you arrive into a different terminal than CO on NW you can most likely go to the CO terminal on the ground and access the club. I imagine that NW has a lounge close by for it's WBC customers.

The P-club is nice, but a bit small. It is located in the south terminal building on the 5th level of the departure hall right next to the U.S. Airways lounge. I would recommend going to the other affiliate lounge. The P-club has showers, snacks, and about 3 work stations. I didn't notice any internet connection. The shower facilities were extremely tidy. I'm sure more information will be avalible.

Sorry I couldn't be of more help.