I'm glad he is back home safe, but I'm afraid the "new" owner is guilty of extortion. I completely understand that they may have bought him in good faith, but a stolen horse is a stolen horse and they cannot by law demand payment from the original owner. Its exactly the same if you buy a stolen car in good faith.
disgusting behaviour by loaner and police
He was on loan, his owner still owned him, she lent him to the person who demanded £2000 for his return and the police were there