what distinguishes above - and *Prime Suspect 3* as well, another Brit cop series produced, interestingly enough, for British commercial tv - from US shows such as *Homicide* is that it/they are not about defense of law and order, made more 'realistic' sometimes by occasional failure, acknowledgement of injustice, and 'human' cops, but about the ambiguity of police work and the concept of police itself - a state with police is to some degree a police state...
in *Suspect 3*, the suspect doesn't walk because the detective couldn't break his alibi, but because the police officialdom has made it impossible for her to pursue the case (in the series, this character has lousy sex with lousy men, is a chain smoker, and has an abortion to advance her career)...
in *Between the Lines*, the main character is a philanderer who betrays both his wife and the woman with whom he is having an affair, in addition to the way he covers things up to protect other officers, compromising cases along the way...the series depicts the secrecy and anti-social solidarity of cops...this character, whose job it is to ferret out lies, lies himself all the time...Michael Hoover
btw: the producer of *Between the Lines* has said that the London Metro Police - which offered its cooperation - never tried to force compromises...however, he says that he did have to make a significant compromise: the cops' language had to be altered because it was comprised primarily of cursing...so much for 'realism'...