While Quizmonster's correct that it was McNeile who created the character and was the original 'Sapper', the pseudonym was adopted by Gerald Fairlie who wrote several more BD books after McNeile's death - I had at least one when I was younger.
As McNeile based the character of Drummond partly on Fairlie, we have a case of a writer writing about himself but not in an autobiography. It doesn't say much for Fairlie though, given that BD was a xenophobic, anti-semitic snob.