I just did a google search on Westminster and there is a Catholic Diocese there and there may be a Catholic " cathedral" there that goes by that name. But the famous Wesminster Abbey is Anglican and the seat of the Church of England and Wales. Once upon a time it was a catholic cathedral as were all cathedrals in England until after Henry the 8th and Rome had the falling out over his wish to divorce Catherine of Aragon of Spain because she produced no sons....and Henry had spied Anne Bolyn (sp)who became the mother of Queen Elizabeth I.
This was Westminster Cathedral, which is the Catholic cathedral there. Westminster Abbey is Anglican.