N7 Holloway: why this London postcode has the number 7

After Highgate, before Hornsey

Holloway is N7 because of the alphabet. N1 is the Northern district office, and in the Post Office's list of March 1917 the offices after it follow by name: Holloway comes after Highgate (N6) and before Hornsey (N8).

See N7 on the map