In the original script Crims was about a 35 year old man pretending to be 19 in order to be sent to a young offenders' institution rather than prison. This plot was dropped right before production began, but the show's producers decided to keep Elis James to play the 19 year old character, despite his obvious years.
Elis James used to do chin-ups on the tube on his way to film episodes of Crims in order to prepare himself.
This was Elis James' first big acting job but it was unfortunately short-lived due to his radio co-host John Robins jokingly calling it "crimes" on air. This caused #crimes to trend on Twitter while #crims was nowhere to be seen. The BBC took this as a sign that not even fans of James were taking the show seriously and they cancelled to show after 1 series. James and Robins are now friends again and hosting a new radio show together as of 2020.