I sold my car on ebay 'Sold as seen'

storeton

As a dealer the buyers right far outway the sellers,as a private mush you need to check with Trading Standards at your local town hall.
It is they who will decide who is in right not police as is not in their jurisdiction
Basically trading Standards are most interested in safety factor of vehicle and were any faults found after sale of which you knowingly knew about?
Remember it's not only second hand car dealers that can be accused of being economical with the truth,that's not to say you or I are not genuine vendors

pinkshoes

Points in your favour:

1. He spent over 2 hours inspecting it.

2. He test drove it.

3. He found an additional fault, and re-negotiated a price to include this fault. He could have rejected the car and walked away.

4. He returned X hours later to collect his own car, you picked him up from the station, and he didn't even mention any problems, thus he/his friend had had a further X hours to inspect it.

5. You issued a receipt that stated most of the above.

Personally I'd just leave it. It's not a police issue as it's a civil matter, although if they harass you in any shape or form, feel free to call the police!

EDIT: I'd consider saying that as a gesture of good will, you'll accept the car back, but they will first have to pay for an independent inspection to prove that they haven't tampered the car or altered it in any way.