I was behind a 2008 model Focus tdci yesterday coming off a roundabout and suddenly there was a smoke screen so big and dense I could not see anything at all! It was pretty scary and I braked and so did the other cars behind me. It took a fair while for the smoke to clear and when it did the Focus was still moving but very slowly with its hazard lights on and then it stopped. I have never seen so much smoke from a car and the inside of my car smelt of smokey diesel.Any idea what could have caused it as I am not a diesel owner?