Scrambler. Dry Twotter posted a photo of the turbine conversion prototype C418 (so designated as a double C219).
The engine installed is the Armstrong-Siddeley Double Mamba gas turbine turboprop engine, used mostly in the Fairey Gannet anti-submarine aircraft developed for the Fleet Air Arm in the late 1940's.
The Double Mamba (also known as the Twin Mamba) was a development of the Armstrong-Siddeley Mamba with two Mambas driving contra-rotating propellers through a combining gearbox. Engine starting was by cartridge, however, forced air restart was achieved in flight. One engine could be shut down in flight to conserve fuel.
The engine installed in the prototype C418 was recovered from a derelict RN Gannet.