2006 Rover CityRover cut out completely while running

My car had a new coil pack and leads fitted recently and has a new battery and has been running fine since then until last night while driving the car suddenly cut out completely. Nothing happens now when I turn the key, the car wont start at all. no lights come on, no heater, stereo, headlights, even hazard lights! Although brake lights and interior lights still work!. Please can someone give me some idea of what this might be and make my Christmas by telling me it's cheap to fix!!