E18 Woodford and South Woodford: why this London postcode has the number 18

Last in the alphabet, after Walthamstow

Woodford and South Woodford is E18 because of the alphabet. E1 is the Eastern district office, and in the Post Office's list of March 1917 the offices after it follow by name: Woodford and South Woodford comes after Walthamstow (E17), and is the last of them.

See E18 on the map