Originally Posted by
Aldebaran
In my opinion one of the hardest to obtain, based on annual levels and not on revenue or "by invitation only" is the Lufthansa HON Circle. You need to accrue 600.000 HON qualifying miles in two years.
I second that. You could also add SQ Solitaire PPS Club card.
As of by-invitation only for European airlines you have (to name a few) :
- AF/KL : Club 2000 / Skipper
- BA : Premier
The latter being much more exclusive and providing many more benefits than the former. There are 12,000 Club 2000 members for instance... far from the 2000 initial members of the "Club", even if KL Skippers have being integrated since the merger of FFPs