McG, God Save the Queen can indeed be rendered in any key, but is actually in G, as surely as Bach's toccata and fugue in D minor is in D minor.

I don't think I agree there. The analogy with Bach's toccata would be a particular arrangement of the tune, which would indeed have a correct key. And no doubt the main official arrangement of God Save the Queen for state occasions is in G major.

However a different arrangement - whether that was a formally composed arrangement, or an informal one by some people singing in a pub would still be recognisably the same tune even in a different key. (Of course maybe that last might be more likely to happen to The Soldiers Song)

I note from a book of National Anthems I picked up in a library sale (which does indeed have God Save the Queen in G) that The Star Spangled Banner is given as in Bb - no wonder people complain about it being hard to sing. I think The O'Meara's boss had a point.