QR provides OW access based on cabin J/F and not status. So MH in C is fine, but GGL in BA WTP is not welcome.
Also be prepared that they will scan your BP and may also ask for the ticket number. I have a constants series of questions over my BA ticket at one stage - which was totally self inflicted but brought home that lounge access to them is not a simple green light/red light activity. It is one of those lounge that is excellent, but because the staff to pax ratio is so high, I always get the feeling I am being watched.
Despite that I am a big fan of the SIN QR lounge which is often closer to the BA gates. It is a great lounge where I have never experience any wait for the shower, you can come in place your food order, take the shower and come out to the food if time is short. They also have an excellent grazing buffet of salads, cheese, dips, ME bread etc. The menu is usually excellent and the bar is well stocked - although often the bar staff are a little less experienced. It is everything that Chelsea could be (I think there are no windows either), but is not.
I find the QF SIN F lounge to be like a cafeteria. Lots and lots of tables, food that comes out very quickly and is set up for the mass of QF flights around 7pm and that strange desire that QF passengers no matter where they are in the world, must eat fried squid and have a full multi course meal in each lounge.
KF