Your word against theirs is enough (unless you a are a world famous fraudster) if you refuse to pay the ticket it should go to an "independent" tribunal, whether these are actually very independent or not is open to debate but they do have to take and consider evidence in the same way a court would which means the balance is often in your favour if the council can't prove the machine was working. If others were caught to this adds to your case (if you can contact these others it would strongly help as you could all back each other up).
