Rather synchronistically there was a programme on BBC Radio 4 last night (12.15am today strictly) Anon's Anthem: the Strange Story of God Save The King covering the history and versions of the words and tune of this very song. I don't know if it's available on the BBC web site.

(I wasn't paying real attention to the programme, but I seem to recall that part of the tune was present in a John Bull tune).

Mick