These are the worst things you can do, in no particular order.
1/ "Front" his insurance and give him a criminal record and an endorsed licence.
2/ Buy him a vehicle.
3/ Pay for his insurance.
4/ Assume that the modern driving test is worth more than 2p when it comes to safety or driving skill.
These are the best things you can do, in no particular order.
1/ give him driving experience while sat next to him.
2/ give him experience of skid pan, off road, and heavy goods and other vehicle driving.
3/ give him experience of the mechanical aspects of a vehicle, the physics of motion, etc.
4/ help him to select, buy and insure a vehicle that he can actually afford, where "help him" = a personal loan with fixed repayments and confiscation of the vehicle if he misses a payment.
5/ play the cop, every time he does something illegal, fine him, real cash money (put it in a pot towards his first decent car if you like) while pointing out he is lucky it isn't points on his licence and increased insurance premiums, "it's not fair dad" doesn't work on a copper who just pulled you for crossing unbroken white lines...
A WORKING 17 year old kid can just about afford to buy and run a crap car legally and safely, plus maybe 100 miles worth of fuel a week, plus some basic clothes, and £10 a week to mum for food, that's it.
Stress the fact that it is a crap car, if he sticks it into a lamp post at 30 mph he will maybe lose his legs, get him good and scared.
You are not doing him any favours sticking him in a decent car and picking up the bills and programming him with expectations way beyond his station and false assumptions about invulnerability.
NOT ONE OF YOU PEOPLE has talked about your responsibility as parents to other road users and pedestrians for the carnage your kids are likely to produce.
A reliant robin or rialto is affordable, fixable, economical, within his means, and exactly the kind of vehicle that won't get him into street racing and A&E.
If he doesn't want one, then HE DOES NOT WANT TRANSPORT from A to B, he wants a status symbol, without earning it himself.