My 59 plate Mazda 2 won't start when the temperatures are low (around minus 5 and below). This first happened last Winter. I assumed it was a flat battery (the car hadn't been driven over the weekend so I got a local garage to jump start it and no problems). However it then happened twice more, it wouldn't start very early in the morning but a few hours later, once the weather had warmed up a bit it started. its been into the Mazda dealer twice who say they can't find anything wrong with it. Their only solution was to let them have it overnight and they would try to start it in the morning (which they did, but I'm assuming the temperature wasn't sufficiently low for any problems to arise). Can anyone suggest what the problem could be? I'm worried that the problem will reoccur this Winter (its been serviced and the battery is fine) and as I know nothing about cars I don't know what to ask the garage to do.

Thanks