Solicitors letter time I'd say.
Just have a chat with someone. Might be a waste of time, but 50 quid for a consultation, tell em the crack, he's surely bound to a verbal contract...they'd tell you, and if you have a leg to stand on, drop a letter to him, or registered post, and get the car gone. You shouldn't owe anything legally cause I'd imagine it's him who broke the contract.
Either get it out, or the legal letter will get him moving on it. You have to do SOMETHING anyway. You can't keep waiting on it like..
Just my 2c. Feel free to ignore me lol