As long as you told no lies and did not misrepresent anything then the buyer has no protection at all. I would suggest that you tell him to scrap it as if driven to a scrapper they will pay around £150 anyway - could have done that yourself. In reality if you refuse to take the car back then other than getting trading standards in to sort out misrepresentation or taking you to the small claims court there's nothing they can do.
Seems you were up front and honest so the rest is buyer beware. Remind them that when buying from a dealer the price is always higher as the dealer has more responsibilities when something goes wrong and that is why dealer cars cost more.
You don't have to give him the money back, you have informed him of the issues and he was happy to pay the £150 for a car he had a chance to inspect, simply tel him to F... Off!
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.