I've just checked my 1962 copy of Gg Capt Stradling's 'Customs of the Services', which, by the way, was first published in 1937 as 'Customs of the Service' (note singular). It became 'Customs of the Services' in 1947 when the other Services realised that they couldn't write anything longer than a short post on the website-equivalents of the era. It has 13 pages on saluting but there is no mention of saluting PMs or wives; to me, that means 'don't', but consider your career prospects as you 'don't'. When I was in MoD a new version was being drafted but I don't know how far that got. BTW, Stradling states that one shouldn't salute unforms in a military tailor's window or the National Anthem blaring out of a set being demonstrated at a 'wireless shop'. D*mn, I wish I had read that bit all those years ago; I would have made much quicker progress down the high street.
Jungly
You remind me of a discussion I had in the presence of assorted pongoes and fishheads. I said something along the lines of '.....and it is a tradition in the RAF that....' and a pongo interrupted to say '....dating right back to 1983!' Quite witty for a pongo, I though.