Nonsense. There are Catholic churches named for the ancient British saints throughout the Isles and elsewhere in the English-speaking Catholic world. My parish in LOndon long ago was St. Ethelreda's (Aetheldreda), and my father was baptised in County Donegal in a church named after an ancient Celtic saint.
"My parish in LOndon long ago was St. Ethelreda's (Aetheldreda)"
Well bully for you