Driving home from a work do yesterday, about 10.00 in the evening, I was following an ambulance - the big car type rather than the van type. It was pootling along, no sirens or anything. Just past a big junction, it pulled into the side and stopped. No signals or anything. I went to overtake and as I was just passing it, it put it's siren on and pulled away from the kerb at some speed. Had I been a yard iurther forward it would have hit me. I was quite shaken. i suspect the driver had completely failed to see me - it was really dangerous. I thought these drivers were supposed to be highly trained - this one evidently wasn't.