At about 200 ft after takeoff the engine began to run roughly. The pilot elected to abandon the takeoff so that the aircraft could be landed on the remaining length of runway. After a high flare for landing the aircraft touched down heavily. The left landing gear leg was broken off and the aircraft came to rest off the left side of the runway. The relative humidity was assessed as being around 80% and there had been recent light rain at the aerodrome. The pilot reported that the aircraft manufacturer considered carburettor icing as the cause of the rough running.