The release of The Casebook of Sexton Blake has prompted me to dig out this example of a Sexton Blake spin-off strip. Blake featured in Knockout from 1939-60 and in Valiant in 1968-70. A later revival stumbled at the last minute: Blake was meant to be the lead strip in Tornado when it launched in 1979 but the failure of the Sexton Blake TV series Sexton Blake and the Demon God in late 1978 led the editors to change Blake into a new character called Victor Drago. A real shame as it was the most true-to-character Blake strip ever.
The lack of a Gwyn Evans yarn in the book reminded me about a spin-off strip featuring one of Evans' most popular creations, Splash Page, a crime-busting journalist who often featured in Evans' Blake tales. A Splash Page comic book was planned in 1949 but never appeared. He did, however, appear briefly in the pages of Comet in 1950 (perhaps using up storylines that had been written by Richard Chance for the mooted comic book).
The artwork was by Alex Oxley, a cartoonist, animator and illustrator who was an irregular contributor to comics during the 1950s. The example below is scanned from Knockout Fun Book 1956 but reprints a 1950 strip from Comet, probably Oxley's earliest comics work.
(* Splash Page © IPC Media)