Smudge,
I think we've got our wires crossed a bit ! Of course, all the Dominions were behind us to a man in 1939. But they weren't our Allies - they were us ! There was no question in anybody's mind that they would even dream of doing anything else.
My faint concern was whether the same would hold good tomorrow (South Africa ?) if the need arose.
The "Wild Colonial Boys" were renowned in the RAF ! (The New Zealanders in particular punched far above their weight in population).
D.