Brown plastic switch by Wylex. Marked 'Water Heater'.
As with many of the items featured, this one has white emulsion paint on it.
The front cover is secured with two small screws either side of the switch. Inside, the terminals are clearly marked, with line on the right and neutral on the left. The remains of some old rubber insulated wire can be seen in the top left terminal.
The switch itself has an 'OFF' and 'ON' legend embossed into the handle, the ON wording highlighted with red paint.
Cables entered through the two oval holes, which require that the switch is either mounted onto a wooden block, or the cables are sunk into the wall. There are two thin plastic sections in the edge immediately above and below the holes which could be removed to allow surface fixed cables to enter.
The back of the switch has the markings 250 Volts, 20 Amps, For A.C. Only, Non Track, Wylex Patents, Made in England and the round Wylex logo.