Not really a Flashman novel, but it does feature Harry Flashman as a major character, and uses the same technique of conveying the feel of a historically-interesting context — in this case, England just before the outbreak of the First World War — through the exploits of an only-just-fictional character. And Mark Franklin is definitely not Flashman, which makes a refreshing change.
I do miss the footnotes, though! Their lack makes it less obvious which details are fictional and which aren't — although that did give me an excuse to go away and read about the events it's talking about in more detail, and perhaps that was the intent. Highly recommended.
ISBN 0006470181.