I can think of a handful who wrestled in UK, clearly limiting myself to proper masked wrestlers, not fly-by-nights:
The Ghoul
The Exorcist
The Outlaw
Le Bourreau de Béthune
And of course giving a wide berth to Mexicans who would do my head in.
Unsure about The Professor and 1973 Black Angel.
Any others?
did Charlie Scott as Bula ever unmask ?