The purpose of the flight was dual training for a private pilot on the aircraft type. On arrival overhead the aerodrome the wind was assessed as a north-westerly at 10 - 15 knots. The pilot joined the circuit for runway 35. The instructor reported that the approach was normal other than being slightly high but this was corrected by the pilot. Touchdown was reported to be on the main wheels first at approximately 65 - 70 knots. As the nose contacted the ground, the aircraft began to veer substantially to the left. The instructor took control using right rudder but with no effect. The aircraft swerved off the runway and the nosegear collapsed. A post accident inspection showed scrub marks on the nosegear and left maingear tyres consistent with left yaw and right rudder application. The nosegear trunnion had failed in sideways overload. A post accident inspection of the aircraft did not reveal any mechanical defects that may have led to the accident.