John Simm's resemblance to Don Knotts
I don't know how well known the series is outside the US, but the Andy Griffith Show was highly popular during the 60's and in reruns to this day.
One of the main characters was a sheriff's deputy named Barney Fife, played by the actor Don Knotts. Barney was probably about the most incompetent "law officer" in the history of tv or film (he made Inspector Clouseau seem Nobel Prize-worthy by comparison).
To me, John Simm looks so much like Don Knotts that I have to keep reminding myself that his character is actually meant to be a highly competent cop!