The sheet music definitely states 106 tunes in the selection.
The 'hidden' 107th tune, though, is from an entertaining piece
called "The Policeman's Holiday", by Montague Ewing; it's not A. E.
Durandeau's song "Ask a P'liceman".
Ewing's tune of 1911, described as a one- or two-step, is almost
like a character piece with an emphasised steady plodding beat.
The phrase quoted by Ketelbey is a two bar interlude, which occurs
several times in "The Policeman's Holiday", and is meant to be
whistled, or sung with the words "Steady, boys, here comes a bobby!".
Possibly it was in vogue when Ketelbey wrote his selection, or it
could have origins older than 1911 and was only being quoted by
Ewing in the same manner, who knows? I enjoyed hearing Frank Himpsl's
MIDI file of the piano roll.