What isn't mentioned in the Guardian article is the numerous changes as to how crime is recorded and what those changes were. Recording crime and how it's been done has been changed by governments over the years to suit their own political agenda which is designed to always show an improvement.
Unless the methods used remain constant, then the data is statistically impotent.
Also, what is a crime in the eyes of the law has changed.
For instance, if someone is given a police warning for a minor offence, it's then not recorded as a crime where as previously it was.
My point is not that crime may have or may not have fallen or remained constant, etc, it's that the graph is pretty much meaningless.