A diocese, also known as a bishopric, is an administrative unit under the supervision of a bishop. The Diocese of Westminster is considered the mother church of English and Welsh Catholics, and although not formally a primate, the archbishop of Westminster is usually elected President of the Catholic Bishops' Conference of England and Wales providing a degree of a formal direction for the other English bishops and archbishops.
From the time of the English Reformation in the 16th century, with Catholicism becoming illegal, there were no Roman Catholic dioceses in England and Wales, with several apostolic vicars, bishops of titular sees governing not in their own name, as diocesan bishops do, but provisionally in the name of the Pope, being appointed instead. However, with the passing of the Catholic Relief Act 1829, legalising the practice of the Catholic faith again, Pope Pius IX recreated the Catholic Church diocesan hierarchy on 29 September 1850 by issuing the papal bull Universalis Ecclesiae. The Hierarchy in Scotland was restored in 1878.
Two Catholic dioceses, those of Leeds and Portsmouth, share their territorial name with Anglican dioceses, the Anglican Diocese of Leeds and the Anglican Diocese of Portsmouth respectively. However, in both cases the dioceses cover differing areas.
The Roman Catholic Church in Scotland comprises two Latin ecclesiastical provinces each headed by a Metropolitan archbishop. The provinces in turn are subdivided into 6 dioceses and 2 archdioceses, each headed by a bishop or an archbishop, respectively.
There is an Apostolic Nunciature to Great Britain as papal diplomatic representation (embassy-level) to the British authorities (UK)