In the Commonwealth realms, a Royal Style and Titles Act is passed in order to declare the Sovereign's formal title.
The most significant of these Acts is the Royal and Parliamentary Titles Act 1927, which was passed in the United Kingdom in recognition of the creation of the Irish Free State, a development that necessitated a change in King George V's title.
The 1927 Act was amended by:
George VI by the Grace of God of Great Britain, Ireland and the British Dominions beyond the Seas King, Defender of the Faith
Elizabeth II, by the Grace of God of the United Kingdom of Great Britain and Northern Ireland and of Her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith
The Act signified a change in the way that the Crown in the United Kingdom related to the Crown in other Commonwealth realms, opened the way for the monarch to have a different title in each Dominion.
Interestingly, in December 1952 the Dominion governments agreed that the practice of separate titles should continue in the reign of the new monarch, Elizabeth II. Each country adopted its own titles; the British Act of Parliament clearly stated that it applied only to the United Kingdom and those overseas territories whose foreign relations were controlled by the UK government. For Britain, the act also tidied up use of the title of King of Ireland, following Ireland's declaration as a republic in 1949. Henceforth, Elizabeth would be known in the UK as Queen of the United Kingdom of Great Britain and Northern Ireland rather than of Great Britain and Ireland separately.[1]