Aren't public spaces such as this determined to have a maximum occupancy for fire reasons? At least in the US they do. You'll often see a plaque of some kind near the entrances to lounges but also restaurants, bars, nightclubs etc.

Personally if I can't find somewhere to sit in the lounge I'll be heading to a different one or the public area. Just because you have status or are flying a premium cabin it doesn't mean that's where you have to wait. Last year I was flying Austrian out of Newark and the LH lounge there is so terrible the wife and I walked straight out and preferred to sit by the gate...at Newark! That's a gauge as to how terrible and busy that lounge was, especially after having come from United's Polaris Lounge!

Thankfully I'm yet to have to walk out of the Terminal 5 lounges, although I did look to abandon the First Lounge at JFK the other week when it was heaving, alas the Alaska Lounge next door was closed to Priority Pass and in the 90secs it took to me to leave and come back a lot of people had left.