5. c. 4) was an act of the Parliament of the United Kingdom that authorised the alteration of the British monarch's royal style and titles, and altered the formal name of the British Parliament and hence of the state, in recognition of most of Ireland separating from the United Kingdom as the Irish Free State.

However, six north-eastern counties, all within Ulster, remained united with Great Britain as Northern Ireland.

The King's title, proclaimed under the Royal Titles Act 1901, was: "George V, by the Grace of God, of the United Kingdom of Great Britain and Ireland and of the British Dominions beyond the Seas King, Defender of the Faith, Emperor of India"[2]At the 1926 Imperial Conference, it was agreed by the Imperial government at Whitehall and those of the various Dominions that the existing royal style and titles of their shared monarch "hardly accorded with the altered state of affairs arising from the establishment of the Irish Free State as a Dominion".

[2] The Conference concluded that the wording should be changed to: "George V, by the Grace of God, of Great Britain, Ireland and the British Dominions beyond the Seas King, Defender of the Faith, Emperor of India"[3]Under the existing constitutional arrangements of the British Commonwealth, it was necessary for legislation to be enacted by the Parliament of the United Kingdom in order for the royal style and titles to be altered; the resulting Act would then extend automatically into the law of the various Dominions.

The proclamation followed the recommendation of the Imperial Conference by altering the Latin and English forms of the existing royal style and titles, the former by replacing "Britanniarum" with "Magnae Britanniae, Hiberniae", and the latter by replacing "the United Kingdom of Great Britain and Ireland and of" with "Great Britain, Ireland and".