Almost defo electrical in nature not fuel, so the finger would point first at the most common thing being coilpack breaking down.
I would let the AA warranty take the car in as faulty, let them do all the guesswork, and spend all the money if I were you, it could indeed be loads of things, even leak leads even though new, silicone gel should really be applied to, leads that sit in hot places like this, down a well so to speak otherwise the can track chronically, unless you are using BOSCH plugs ?, if you are junk them and put ford/NGK ones in instead, famous for doing this on zetec, had it myself twice.
tabetha