Britmac light switch.
Part of the Bob Gray collection of electrical objects.
Britmac Circular toggle light switches such as this model by Britmac were produced in large numbers during the rapid increase in the take-up of electricity during the 1920s and 1930s. They could be made cheaply and in large numbers from moulded Bakelite. Bakelite is a lightweight chemically-produced product. It is non-conductive and also waterproof so that is why it was chosen for making electrical fittings.