There was a meeting of Prime Ministers of the Empire in London in December 1952.
This meeting is now known as the Commonwealth Heads of Government
Meeting aka C.H.O.G.M.
At this meeting, it was decided that each Commonwealth would be granted permission to designate the style and title of their monarch.
It was also decided @ this meeting that Elizabeth would be next in line to the throne.
1953, England passed the Royal Style Act that statutorily gave the
aforementioned permissions. This Act was the first proclamation of
READ THE UNITED KINGDOM ROYAL TITLES ACT 1953 HERE
Most, if not all Commonwealth nations
followed suit with the Menzies liberal government passing it in
Australia, later that year.
READ THE AUSTRALIAN ROYAL STYLE AND TITLES ACT HERE
The office of the Queen of
England, Australia and her other realms was included in Australian
statutes for the first time.
The 1973 Royal Style and Titles Act
amended the 1953 Act removing the United Kingdom from the title "Elizabeth
the Second, by the Grace of God of the United Kingdom, Australia and
her other Realms and Territories Queen. Head of the Commonwealth,
Defender of the Faith".
You can read some background material gained by a friend of mine by