An inter-club fly-in had been organised at the private airstrip. The club secretary who had organised the meeting had expressed an interest in aerobatics, and arranged to accompany the pilot on a demonstration flight. A series of aerobatic manoeuvres, judged by the witnesses to be of a relatively poor standard, were completed between about 1500 and 3000 feet above ground level. The aircraft was then observed to overfly the aerodrome at about 300 feet agl and enter what appeared to be a roll. When the aircraft reached the inverted attitude, its nose was well below the horizon and the roll was not continued. The nose then lowered further as a "pull-through" manoeuvre was apparently attempted, however the aircraft impacted the ground at high speed before level flight could be regained. Subsequent investigation indicated that the aircraft and its control systems had been serviceable prior to impact with the ground. The pilot was neither approved nor sufficiently experienced to perform aerobatics at a low level and it is probable that on this occasion his actions were influenced by the presence of the group assembled on the ground.