Wall boxes
Overview
Wall boxes are so-named as they are designed to be built into a wall. This can be an exterior wall of a building or wall enclosing a property. Being (apparently) cheaper to manufacture than a pillar box, in many areas they were built into a dedicated brick column. They are no longer manufactured, having been largely superseded in low-density areas with lamp boxes. Lamp boxes can even be found embedded in both walls and brick columns just as wall boxes were designed to be installed.
In southern UK at least, the vast majority of wall boxes seem to have been supplied by W T Allen & Co of London.
Examples