Conversation so far:
What was John Harrison's first novel?
His first short story was published during 1966 by Kyril Bonfiglioli at Science Fantasy magazine.
Did he write in any other genre before writing Science fiction?
CANNOTANSWER.
How popular were his first stories?
His first short story was published during 1966 by Kyril Bonfiglioli at Science Fantasy magazine, on the strength of which he relocated to London.

Question: Who influenced him as a writer?
Self-contained rewrite: Who influenced John Harrison as a writer?