I received a letter from Northern rail about an incident that occurred at Burley in Wharfedale. I had bought a ticket but I left it on the train. As I got of the train and left the station into the car park. I was stopped by a member of staff doing a ticket check. I looked through my pockets as I thought I still had the ticket on me I produced what I thought was the correct ticket but the man took this from me as it was the wrong date. he then asked me to step into the station and took my details, he said 'don't worry, you're not in any trouble mate.' I have now received a letter asking me to say what happened and they say they will prosecute if I don't reply within 14 days, this was about 4 days ago. I don't know what I should do. I don't want this to go to court.