The postcode area originated in 1857 as the SE district. In 1868 it gained some of the area of the short-lived S district, with the rest going to SW. It was divided into numbered districts in 1917, by giving the district closest to London that hosted the head office the suffix "1" and all others alphabetically based on a locally important parish, chapelry, topological or built environment feature administering or close to the local distribution office. SE28 is a late addition carved out of the existing districts SE2 and SE18 to reflect the building up of a new London district in what had been the meadows and marshes by the tidalThames in the parish of Plumstead: Thamesmead. Unlike SW, where a consecutive 50%, there ten, districts can more officially be traced into two alphabetical groups excluding SW1, SE has always technically followed the norm in that SE1 is the only head district. However SE19 was drawn up to serve the key distribution office serving Norwood after a complete alphabetical series so that those surrounding it and SE21 : SE20 and SE22 to SE27 are strictly alphabetical afresh but it has never technically been a "head district". The postcode area is part of the London post town. There are no dependent localities used in the postcode area. SE1P is a non-geographic postcode district for PO boxes located in SE1.
The approximate coverage of the postcode districts, with the historic postal district names shown in italics: ! SE1 ! style="background:#FFFFFF;"|SE1P ! SE2 ! SE3 ! SE4 ! SE5 ! SE6 ! SE7 ! SE8 ! SE9 ! SE10 ! SE11 ! SE12 ! SE13 ! SE14 ! SE15 ! SE16 ! SE17 ! SE18 ! SE19 ! SE20 ! SE21 ! SE22 ! SE23 ! SE24 ! SE25 ! SE26 ! SE27 ! SE28
Boundaries
SE1 has a very long tidal Thames frontage and is in Central London as is SE11 named after Kennington, close to Westminster. SE2–SE18 spread across the north and east of the postcode area; enquiring into their naming system explains how SE2, SE7, SE8, SE10, SE16 and SE18 also front the river. Postcode districts SE19–SE27 form a group in the southwest. Addition SE28 is in the northeast corner of the first group. The postcode area maps roughly to the combined area of the London Borough of Southwark, London Borough of Lewisham and Royal Borough of Greenwich. the eastern part of the London Borough of Lambeth, the northern part of the London Borough of Croydon, the western part of the London Borough of Bexley and the northwestern part of the London Borough of Bromley are within the postcode area. In 2002, some residents in West Heath, a slight projection with neighbouring areas, wished to have their postcodes changed from SE2 to the adjacent DA7 postcode district, citing higher insurance for their houses, belongings and cars as reasons to change. Royal Mail has said it will not consider changes to postcodes for these reasons.
