White plastic double pole switch by Wylex.
The switch lever has the ON/OFF engraved markings, and these are both highlighted in brown paint.
Only one of the holes in the rear casing has been used, as the other cable was surface mounted. Unusually, the supply cable was surface fixed and entered at the top of the switch, with the flex to the heater passing through the back of the switch and concealed in the wall.
The earth terminal is not shown, but is identical to that on the brown switch.
Zoomed pictures are smaller, as these pictures are much older and the camera used was significantly lower resolution.