I seen that until 26th March 1953, the Queen's Royal Style was, "By the Grace of God, of Great Britain, Ireland, and of the British Dominions beyond the Seas, Queen, Defender of the Faith"
It was only later that the United Kingdom and Northern Ireland were mentioned in her Style.
It seems there was no United Kingdom in the Twentieth Century under three and a bit Monarchs, the current Queen and Kings George VI, Edward VIII and George V.
Perhaps then, it could be just GB & NI with no Scotland?