The pilot was intending to fly to Goodwood Airport in Sussex. During the pre-flight checks the pilot noticed that he had to apply the right brake pedal more firmly than normal when turning to the right but that the operation of the left brake pedal appeared normal. The aircraft entered Runway 28 and taxied towards the Runway 10 threshold prior to takeoff. As it approached the intersection with Runway 04/22 the pilot applied both left and right toe brakes evenly, but rather than maintaining direction, the aircraft suddenly turned to the left. The pilot tried to release the left brake whilst maintaining pressure on the right brake in an attempt to control the turn, but the aircraft ground looped; the right landing gear collapsed and the propeller and right wing struck the runway. The pilot shut down the engine and exited the aircraft. He noticed there was a fuel leak and moved away from the aircraft prior to the arrival of the AFFRS. The pilot considered that the cause was a loss of right brake effectiveness.