NW10 Willesden: why this London postcode has the number 10

Last in the alphabet, after The Hyde

Willesden is NW10 because of the alphabet. NW1 is the North Western district office, and in the Post Office's list of March 1917 the offices after it follow by name: Willesden comes after The Hyde (NW9), and is the last of them.

See NW10 on the map