What’s the origin of the phrase ‘Sexton Blake’?
This is Cockney rhyming slang - the rhyme being with ‘fake’. Londoners might refer to something of dubious origins as a sexton.
Sexton Blake is a fictional detective who first appeared in the The Missing Millionaire, written by Harry Blyth (a.k.a. Hal Meredeth), in The Halfpenny Marvel #6, December 1893. The character has since appeared in thousands of stories, by many different authors.