Westminster Abbey

Westminster Abbey is not a cathedral but a Royal Peculiar.

"A Royal Peculiar (or Royal Peculier) is a place of worship that falls directly under the jurisdiction of the British monarch, rather than a diocese. The concept dates to Anglo-Saxon times, when a church could ally itself with the monarch and therefore not be subject to the bishopric of the area. Later it reflected the relationship between the Norman and Plantagenet kings and the English church. " Wikipedia