The pilot had experienced a smooth flight and after checking the wind direction positioned the aircraft on the downwind leg for a normal circuit. He reported that after reducing speed he lowered one stage of flap and then selected the landing gear down. He believed that he also checked the gear indicator on final approach and saw three green lights. The speed on final was reported as about 80 kts with a power setting of 16 inches and full flap. After round out power was reduced to idle and the pilot then sensed that the aircraft was settling further than usual. When the propeller began striking the runway the pilot pulled back sharply on the control column and applied full power. The aircraft failed to respond as expected and the pilot turned to the left away from the strip. Shortly afterwards the aircraft mushed into the ground. Ground witnesses reported that the aircraft made an approach with the gear up and that the gear began to extend when the pilot pulled up in his attempt to go around. The aircraft gear was fully or partially extended on impact and the main legs were torn off. The aircraft came to rest some 300 metres from the centreline of the runway. Initial on-site inspection could not find any reason for the failure of the gear to extend and showed that the gear warning horn was operable.