The song, although humorous, also reflects some of the hardships of working class life in London at the beginning of the 20th century.
Thereafter, she reflects that it would be ill-advised to approach one of the volunteer policemen (a "special"), as they are less trustworthy than a regular police constable (a "copper") and might take advantage of her inebriation.
Alternatively (according to the physical gestures accompanying the song) they may simply be less qualified to give dependable street directions.
There are a number of alternatives to the last two lines: Various lineups of the Clancy Brothers (with Tommy Makem, Louis Killen, and Robbie O'Connell at different times) have performed the refrain as part of a medley, immediately following "They're Moving Father's Grave to Build a Sewer", which also deals with the travails of working class Londoners.
The narrator responds aggressively and reveals a negative opinion of all fans of that club, using obscene language.