I’m afraid that ignorance of the law is no defence.
The vehicle must be taxed tested and insured or you must make a Statutory Road Notification.
If he sold the car without advising DVLA of the change of keeper he commits a further offence.
This is an offence of strict liability, either he did it or he didn’t and if he didn’t, he commits an offence.
What will happen? He will get a fine. A couple of hundred pounds probably at most.
He will not get any points on his licence and he will not lose his licence and he will not go to jail. It doesn’t have any long-term ramifications, only financial ones.
He would be better holding his hand up and saying that he pleads guilty because he just didn’t know the process.
Thank you for letting me assist you with your legal question. I am glad that I was able to help.
I am not certain whether that answers the question for you or not, but I am happy to answer any specific points arising from this.
It will be my pleasure to help you again either further with this or any future questions you have