Which cathedral was established or dedicated first, Chelmsford Cathedral or Cathedral of St John the Evangelist, Portsmouth?
Chelmsford Cathedral:  It became a cathedral when the Anglican Diocese of Chelmsford was created in 1914 and is the seat of the Bishop of Chelmsford. Cathedral of St John the Evangelist, Portsmouth: The Cathedral Church of St John the Evangelist (also known as St John's Cathedral) is a Roman Catholic cathedral in Portsmouth, England. Cathedral of St John the Evangelist, Portsmouth:  It was dedicated on 10 August 1882.
The Cathedral Church of St John the Evangelist