Saluting Ladies...
...is a bit old school and should probably be regarded as rather patronising. However, saluting a bridal party is de rigeur regardless of rank, commissioned status etc.
To continue the film references. 'In Which We Serve' (a shameless propaganda piece from about 1942) is a useful example. It features Noel Coward(sp?) as a RN Captain meeting a Petty Officer and his new wife on a train.
As he is in uniform and behatted the Capt pops one up to the new Mrs PO. Of course it's not a proper military salute but one of those shifty looking hidden palmed RN abortions but you get the picture. Bottom line is if you want to salute the ladies then their husband/life partners' rank isn't an issue.
As for the PM, it's only polite to salute snr Civil Servants when you meet them and he is the head of the civil service.