Continuity mistake: In several episodes of the show, Richard Beckinsale's hair changes length and style during individual episodes.
Suggested correction: Not a mistake. The show takes place over more than a year in the prison. People change their hairstyle and length during that time. Just because episodes are next to each other does not mean they happen within a very short period of time.
While the mistake is vague and should include a specific example or two, the mistake is saying that within an episode the hair changes, not that the hair changes between episodes.