Accession Declaration Act 1910
The Accession Declaration Act 1910 is an Act which was passed by the Parliament of the United Kingdom to alter the declaration that the Sovereign is required to make at their accession to the throne as first required by the Bill of Rights 1689. In it, they solemnly declare themself to be faithful to the Protestant faith.
Source: Wikipedia — Accession Declaration Act 1910 (CC BY-SA 4.0)