In message , Paul Corfield
writes

SW11 surely if you're referring to Battersea?

Edward was referring to Vauxhall, which comes under SE11 (Kennington
postal area). It is adjacent to SW11 (which is Battersea).

The way that London postal district numbers developed has a strange
logic, largely based on the location of head sorting offices (and the
whims of Anthony Trollope).
--
Paul Terry