I wasn't there, of course, and so can't be entirely certain, but I'm going to guess that this little group was snapped sometime not too early in the evening. Not too late, of course - they're all still presentable - but in that sometimes dangerous stretch when everyone is still more or less coherent, but it's not at all clear that things are going end well.
Miss Kendall, for example, would appear to have had just about enough of whatever it is Miss Bacall is going on about, and there's something ominous in Viv's (surprisingly jowly) look of discontent. Were I Noël Coward, I might suddenly remember an appointment, or perhaps claim to spy poor Princess Margaret all on her ownsome on the other side of the pub. However charming, individually, the ladies involved, this is one conversation from which the getting is good.