after having problems with my engine conversion 'specialist' i checked up with trading standards and you can remove your car at any time but you do have to pay for all work done up to that point.if you take it back and refuse to pay then he can call the police and they will stop you from removing it.deciding on how much should be paid is another matter altogether but as long as you are offering to pay something the police wont stop you and it then becomes a civil court matter to sort out the value of work done. or you could just turn up mob handed unannounced and take it back forcefully