X reg Ford Mondeo LX burning smell and smoke!?

My son and I could both smell an electrical burning smell in the car, which had been driven for about 20 mins. Then, smoke started coming out from the drivers side of the engine at the front, through the grille and from underneath the bumper. I turned the engine off immediately and the smoking stopped. Called a repair man who couldn't get the fault to replicate or find anything wrong. A bit unnerving as now I'm waiting for it to start smoking again, or even worse, burst into flames! Anyone got any ideas? Many thanks.