Unsurprisingly, "Maybe It's Because I'm A Londoner" was written by a London songwriter. Hubert Gregg was born in 1914, and his main profession was a BBC radio presenter. The song was his second hit; his first hit was also about London. Equally unsurprising, Gregg used the same title for his autobiography; like Noël Coward's "London Pride" the song was written as a morale booster during the Second World War, although it didn't see the light of day until 1947 when he was asked by bandleader Jack Hylton if he had any songs suitable for Bud Flanagan.
This was chosen by the actor Jack Warner and the producers of the TV series Dixon Of Dock Green for its theme music, although it was later replaced by "An Ordinary Copper".
The song earned Gregg the Freedom of the City of London, and was also adapted rather than parodied as "Maybe It's Because I'm From Liverpool", which was popularised in Australia by the English comedian Arthur Askey.
Suggestion credit: Alexander Baron - London, England, for all above