The pilot reported that while in the cruise at approximately 1,700 ft amsl he selected the carburettor heat ON and the engine lost power (decreasing from 2,300 to 1,500 rpm). Selecting the carburettor heat OFF had no effect so he reselected it ON. He moved the throttle lever backwards and forwards and selected a different fuel tank but neither action restored power. He transmitted a distress call to Yeovilton Radar and then concentrated on landing in a suitable field.
The aircraft touched down in the pilot’s chosen field at 60 mph but bounced back into the air when it ran over a bump. It touched down again and the pilot began to brake but he was unable to bring the aircraft to a halt before it struck an obstacle and turned onto its back. The three occupants vacated the aircraft through the normal exits.
It was not determined why the engine lost power.