Strake,
Unless you plan to hi-jack the plane, I don't think you'll be going to Beijing, VS fly to Shanghai Pu-Dong (PVG). Hope this doesn't upset your plans
Re the limo's at the downroute location, there'll be people with Virgin Upper Class signs to assist you, and if you're not sure, look for a red uniform in arrivals/ bggage hall.
At LHR T3, go straight ahead when you come through the doors from Customs and you'll see the Limo desk in front of you.
Have a great trip