Ford Mondeo smoking

Car was running perfectly. Next time I went to use it, about 90 minutes later, the starter motor 'hiccupped' as if low battery. Car then started, but sounded rough and missing. By the time we got 20 metres up the road, thick WHITE smoke was pouring from the exhaust, almost like it was alight! The smoke smells like burning, as opposed to the smell of normal exhaust smoke. I know it's serious, but no idea how bad. It has oil and water in, and can see no leaks. It's a 2 ltr Zetec engine, single cam.