Is there anyone who will stand up as a witness for you ? just go and tell the judge/magistrate exactly what happened and you were doing your duty as a good citizen. whatever happens you wont go to jail for first offence but dont make it easy for them plead not guilty and have your say.Say it quietly and dont loose it in court, just tell them what happened, dont bad mouth the police it wont go in your favour, tell them in your own words and take your time so you explain it properly, it will be scary but after all you have nothing wrong.good luck and let us all know the outcome.