Gambling contracts became enforceable in 2007, which means Betfair could indeed pursue you through the courts. Nitin Khandhia, director in the civil litigation and dispute resolution department at BTMK solicitors, reckons the fact that Betfair handed over the money before the mistake was realised does not affect its right to recover it. If you are determined to fight, he suggests you try Betfair's internal dispute resolution service and, if that fails, the Independent Betting Adjudication Service. However, if Betfair has not mentioned legal proceedings it might have decided it's not worth the hassle, but do keep an eye on your credit rating.