SE17 Walworth: why this London postcode has the number 17

After Rotherhithe, before Woolwich

Walworth is SE17 because of the alphabet. SE1 is the South Eastern district office, and in the Post Office's list of March 1917 the offices after it follow by name: Walworth comes after Rotherhithe (SE16) and before Woolwich (SE18).

See SE17 on the map