Save that pass!!!! There is a NW/AMEX affiliated lounge at LGW, it's up the escalator, on the second level as you go through immigration check-point. I believe it's called the Sir Robert Hardingham Suite, down a long haal, past the Virgin Club. I used my AMEX Plat to get in when I was there on a run last month. No problem. Adequate club, has a shower if you need it, snacks and drinks. Enjoy!