Sounds like a scam. If it was a genuine private sale, then I believe he has no recourse at all.

If you want to string him along, then you could ask him for an independant engineer's report. He'd probably need something like that to present to a court.

I'm sure Lucy'll be along soon to give solid advice.

Private sales are almost always based on the principle of "Caveat Emptor" - buyer beware - so unless you make a factual mis-statement or the car has been clocked he has very little comeback.

A factual mis-statement might include something regarding the car which can be reasonably called into question with evidence - "four new tyres and shock absorbers" for example "new clutch" or "new brake pads all round". If you could have been shown to misled him an a factual manner then he may have some recourse.

"Excellent drive and condition" is not a warranty as to anything and is something that he could reasonably be asked to ascertain for himself prior to purchase - so Caveat Emptor would apply.

Write to him to tell him you will rigorously oppose his claim should he choose to bring one.

Come back to me if he does. If the total foundation of his claim is "Excellent drive and condition" - he does not have much hope of success.