Unless you're rich, in which case you can just get off by paying the original ticket price, and avoid a criminal record altogether [1]. By punishing innocent mistakes, and mainly operating outside rush-hour, the UK penalty system unfairly targets tourists, the elderly, and anyone else who is unfamiliar with the nuances of all the various rules, prices, etc. It also treats honest citizens like dirt and is wholly regressive and outdated in my opinion.

[1] http://www.theguardian.com/uk-news/2014/apr/13/man-avoids-pr...