The pilot was practicing circuits at White Waltham Airfield. On the second touch-and-go, the aircraft bounced twice and the pilot decided to go around. The airspeed was low and he was unable to arrest a pitch down which caused the propeller and nose to strike the ground. The aircraft overturned and settled on its back. The pilot commented that he should have initiated a go-around immediately after the first bounce; and that wearing four-point harnesses, which were done up tightly, prevented the occupants from suffering any injury.