I'd advise him to start saving hard. And to learn to love public transport. He's looking at charges of driving with no insurance, driving with no tax, and providing a false name. If he's lucky, it will just be a large fine and some points. If he's unlucky, he's looking at a ban.
The friend who owns the car has two options
1) Admit he allowed your son to drive the car, knowing it was untaxed and your son was uninsured. That means he's in line for an unpleasant time in court.
2) Say your son drove the car without permission. That adds an additional charge of theft to your son's list of charges.