Peterborough United are known throughout the world of football as 'The Posh' and the nickname was almost certainly inherited from earlier, unconnected professional clubs in their home city.

Although the present club did not come into being until 1934, the 'Posh' name first came to the fore a decade earlier, almost certainly stemming from Pat Tirrel, player manager of Fletton United, a previous user of the present club's London Road ground, who announced in close season of 1921 that he was looking for 'Posh players for a Posh team' to compete in the Northamptonshire League (later the United Counties League).

Fletton, previously known as the 'Brickies,' re-formed as Peterborough and Fletton United in 1923 and both nicknames were in use through the 1920s, although supporters complained that 'Posh' references were sometimes used by newspapers in a derisory manner.

Peterborough and Fletton United folded in 1932, the present club was formed two years later and a Midland League debut against Gainsborough Trinity on 1st September 1934 was greeted with cries of 'Up The Posh' from the crowd.