The only people who can add that sort of information are the police, which they would do based on their local files. If the police weren't involved, then they wouldn't have anything on you, and they certainly wouldn't go on a fishing expedition around various agencies, local authorities, etc. to see if they can find anything. I wouldn't expect them to have anything to disclose, unless the Benefits Agency chose to tell them at the time, but if the police didn't contact you, that suggests they weren't involved at all.
As Chris Stacey said: Although its not formally part of the sentence that is handed down in court, the criminal record that someone comes away with effectively becomes a second sentence, which can have a long-lasting, if not lifelong, impact.