A good starting point for your friend would be to get the facts accurate. He likely borrowed £3,800. £12,000 is likely the total amount repayable during the loan term, £8,500 is likely the amount remaining to be repaid during the loan term and £4,000 is likely the actual principle debt owed. The latter could easily be higher than the original amount loaned, even after a year of repayments, as there were probably all sorts of fixed arrangement fees added when the loan was advanced, and a number of repayment fees being levied at the end too.
Handing over the car will not end the loan agreement. The company already owns the car. All it would likely achieve would be that they'll sell is a realise a fraction of its actual value plus charge all manner of fees for the privilege of doing so. If there's anything left, they'll take that off the outstanding balance which he will still have to pay.
If I was him I wouldn't panic. He's starting from a position of relevant stability as he had enquired about repaying the loan. Begin by asking for a subject access request on all the data the business holds on him, including copies of the application and appropriate disclosures at the point of sale. While they're taking their 40 day allowance to do that he can look around and see if he's able to consider other options, such as arrange alternative cheaper finance to swap out this horrible 300% APR arrangement with.