PM wrote:

That's about the size of it. They would like to stop him keeping the car
though.

Well that's where a lawyer comes in. Because I'm not sure of what the
difference is and who gets taken as the owner.

As others have pointed out the V5C is irrelevant to the question of
ownership. The problem is as far as I see it that it depends who handed
over the cash for the car. If he did it, then I suspect he is the owner.
If the parents did it they are the owners.

The reason I think this way is that him paying for the car makes him the
owner. Them lending him the money makes them his creditors, but since
they did not create a hire purchase (or similar) agreement they have no
charge over the car. Therefore it is his.

He still owes them the money.

We then get into areas of law I really don't understand which is can
they have a lien over his property? If they do have a lien do they have
the right to sell the vehicle to offset his debt?

I'll support my analogy with an example. I go to my bank and borrow
£5000. I then buy a car for £5000. Does the bank own the car? No. I stop
making repayments to the bank. Do they then have a lien over the car?
No. Do I still owe them £5000? Yes. Can they seize the car and sell it
to offset my debt? Possibly, but not before they have obtained a
judgement in their favour from a court. Then in the event of non-payment
they would have to return to court to obtain one of the following:

A warrant of execution - sending a court bailiff to collect the money.
An attachment of earnings order - stopping the money from wages.
A third party debt order - freezing a bank account.
A charging order - paid on the sale of the defendant's house.

I think that's the position the parents are in, unfortunately. And I
suspect that if Mr B. gets his act together he could have them for theft
if they get hold of and keep the car. They are in a difficult position,
their remedy in law is civil, which means they have to pay, it takes
time and any decision will be effectively unenforceable.

All he has to do is to tell plod they stole his car and they end up with
a criminal record.

IANAL.