When is a purchase a purchase

we had an arrangement with an owner of a caravan that we could take the caravan to an expert to have it checked over before we purchased it. (owner is a work colleague) We found lots wrong including rotten walls, a window falling out. We have tried to arrange to return the caravan to the field where it was being stored, but the owner says as we took it away he considers it sold. We have never exchanged money. This was a couple of months ago now as he keeps stating he does not want it back and it is ours, and he wants the money for it. Where do we stand?

If you didn't sign any paperwork or re-title the vehicle, it still belongs to him. If you did sign papers, it depends on what the papers said. If he clearly understood you were having it inspected before buying it, that's evidence that you wouldn't buy it if it failed the inspection.

I would take a witness with me and park it in front of his house and give him the keys. If he's not home, I'd give them to him at work in front of a witness.