These Morse switches were used in many RAF aircraft during the Second World War. The large button was used to send the correct morse signal via lights on the underside of the aircraft. In the Spitfire and Hurricane cockpits, this is fitted on the right hand side within easy reach of the pilot's hand.
I make the brackets for these as well, to fit this later type as well as the earlier version. Please take a look in the Spitfire parts page.