To add to the above.... as the car wasn't sold without a SORN then it must be considered to be roadworthy, whether you said it was for spares or not. As it had no SORN then it has to be roadworthy. That it has 6 months MOT left is irrelevant - MOT does not give carte blanche to drive a car in an unroadworthy condition. It is merely a statement that the car passed on the day of the test and it is up to the owner to keep the car in a roadworthy condition.
You are stuffed and potentially a criminal.