The aircraft was being restored to flight status, having had a new and larger wing fitted. During a high speed taxi check, the aircraft inadvertently became airborne and drifted off the runway heading. The Pilot, who had not intended to fly the aircraft and who had not flown for six months considered that a safe landing could not be made and commenced a circuit. During this circuit the engine lost power and a forced landing was carried out into a grass field. The subsequent heavy landing caused the nose wheel to detach, destroyed the propeller and led to the collapse of the left main wheel. The Pilot exited the aircraft without injury.