Warranty issue. However, have you tried putting the electronic key into the docking port under the left side of the dash. If the engine starts first time everytime with the electronic key in the docking port then suspect your key needs replacing (or possibly a battery?). If you still get the intermittent start then the fault is in the car itself, brake pedal switch?? or faulty programming of the electronic key to the car.
Just a thought, how far away from the dashboard are you keeping the electronic key? It has a limited range. It works from the passenger seat (obviously as the Jag is primarily a rhd car) but not from the back seat.