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M.K. Electric Ltd of Wakefield Street, Edmonton, London, N18
The company also invented the modern light switch. [evidence?]
Initially the company's sole product was the quaintly-named Multy Kontact socket (hence M.K.). This was safer and worked more effective than the split pin-style sockets that were on the market at the time. The Multy Kontact caught the attention of the British Engineering Standards Association (BESA), which revised its standards to match the levels of self-adjustment and contact-making it introduced, effectively making the Multy Kontact the standard socket.
1926 Added a small electroplating operation to the factory.
1926 Established Insulators Ltd, a partly owned subsidiary which manufactured plastic mouldings for a range of trade customers
By 1928 MK was using the new insulating material Bakelite. MK also introduced the first ever shuttered socket, concealing the socket tubes and eliminating the alarming flash invariably accompanying plug withdrawal from old fashioned sockets. These became the foundation for the British domestic electrical system
1933 Established a subsidiary Knightshades Ltd
1937 Manufacturers of electrical accessories. "M.K." Electrical Accessories. 
WWII The company switched most of its production to detonators, firing systems and centrifuges needed for the war effort. Spitfires, Hurricanes and Lancasters all used MK products.
Early 1960s: the company opened a factory in Southend.
1968 Charles Arnold retired from the chairmanship of the company and sold 25 percent of the equity in the company, retaining 10 percent
1969 Charles Arnold died at age of 83.
1984: 100 millionth Safetyplug was produced.
Also had a factory in St Asaph.
2013 Now part of Honeywell
See here for company history, with a timeline showing pioneering products.