The student pilot of G-BFEK had been instructed to halt his aircraft at a holding point for Runway 27 at Gloucestershire Airport. After waiting for about two minutes, the aircraft suddenly tipped to the right, coming to rest on its right wing tip, right main wheel and propeller. An EC145 helicopter had completed a rotors-running refuel and, after obtaining ATC clearance, was hover taxiing behind the Cessna. Another helicopter, an R44, was on the ground at the nearby Avgas pumps, with rotors running. The EC145 pilot was aware of both the Cessna and R44 and followed a path that gave maximum clearance to both. It was estimated that he passed between two and three rotor diameters from the Cessna. It was concluded that the downwash from the EC145, perhaps exacerbated by the wind speed and direction, caused G-BFEK to tip over.