My favorite bit with Kwik Fit is when they tell people they "cant allow you to drive the car in that condition" when you refuse to have the work they advise you needs doing.
I'm sorry? YOU wont give me the keys to my car back unless I pay you a £300 for discs and pads my car doesnt need as they were only replaced 2000 miles ago?
I think its more a threat to call the rozzers if you leave than a threat not to give you the keys back (if they were telling the truth about the brakes and not making it up it would be a criminal offence to drive the car on the road).