The airline lounges in Asia are better than the USA, even United Clubs. Don't waste your time at a United Club though, go Singapore or ANA (Thai if in a pinch). The food is superb and the beer machine pours a perfect drought.
London City Airport (LCY) is the most convent option for London travel. Unfortunately it's also very expensive and requires a connection for travel outside Europe. It's still worth considering if you were connecting with Lufthansa, KLM, or SWISS anyway.