speeding up when slowing down?

Ok I have a 1.6TDCI Focus on a 14 plate. recently it has started to speed up when slowing down, I am not getting the high revs that others have noticed but when changing down the car just wants to take off especially in 4th and 3rd but will do it through the whole range, my partner doesn't want to drive it as she feels it is way too dangerous. have been back to ford twice but they say they can't find anything wrong, which there is. any help and is this a known issue?