general problems of the 2008 Jaguar XJ

As I was going down a slopping street at approximately 30-35 mph, I stepped on the brakes to slow decline but car surged forward, immediately gaining speed up to 58 mph. When I leveled out at the bottom of the hill I was able to pull over to side of road by tapping on the brakes until I came to a complete stop. Second incident happened two days later. While stopped at a stop sign waiting to turn left, car accelerated forward going from 0 to approximately 30 mph barely missing car coming at me from the left. Was in middle of the road before I knew it. Stopped car as before, light repeated taps on brakes. Car is at Jaguar dealership for inspection.