The pilot was conducting a bore inspection at a height of approximately 300 ft above ground level at the time of the occurrence. He had just flown over the No. 7 bore when the engine started to run roughly. The pilot completed a magneto function check which did not disclose any problems. He decided to turn the ignition switch off and then back on to make the engine backfire in an attempt to clean any lead off the spark plugs. When the pilot attempted to turn the switch back on, instead of the key turning in the ignition, the whole ignition box turned in the dash, leaving the key in the off position. The pilot applied additional pressure to the key and the whole switch became detached and fell inside the dash as the key came out in his hand. He attempted, briefly, to correct the problem, then realising that he was going to have to land the pilot transferred his attention to the emergency landing. The pilot aimed the aircraft between two trees knowing that the wings would be damaged, but hoping the fuselage would be safe. The aircraft went between the trees then skidded for about 10 metres before the propeller dug into the ground and it flipped over onto its back. The aircraft had flown approximately 95 hours since its last periodic servicing and there had been no indications that the ignition switch mountings were faulty during that period. The reason for the rough running was not determined.