Following the Reformation, uniformity was a key principle undergirding worship in the Church of England. The Crown claimed the prerogative to order the use of, and to alter, Church services in spite of the provisions of any Act of Uniformity, the Canons or any Declaration of Assent. This caused confusion among the clergy and others as to who had ‘lawful authority’ to permit such usages or changes. This confusion was exacerbated by episcopal claims to a jus liturgicum. Statute and case law, as well as the wording of the Declaration, also ensured rigidity in doctrinal adhesion. Since the Church of England (Worship and Doctrine) Measure 1974 and recent amendments to the Canons and the Declaration of Assent, this rigidity has been relaxed and clarity provided as to who may authorise services or permit departure from otherwise authorised forms of service.