The Roman Catholic Diocese of Portsmouth is a Latin diocese of the Catholic Church that covers the Channel Islands as well as parts of England. The episcopal see is St John's Cathedral in Portsmouth and is headed by the Bishop of Portsmouth. The diocese is part of the metropolitan Province of Southwark, which covers all of the far South of England as well as the Channel Islands.

The Diocese of Clifton is a Latin Church diocese of the Catholic Church centred at the Cathedral Church of Saints Peter and Paul in Clifton, England.