Three police officers killed when their convoy carrying heroin was ambushed. So began last night’s first episode of series 5. Should they have stopped for the burning car and the woman pretending that her baby was trapped inside? Of course they should, but who was the leak within the police feeding information about the convoy to the drug gang?
These twists and turns in the plot and the excellent performances of the AC-12 officers make the story gripping.

What of the ethical dilemmas? An undercover cop who may have gone rogue. What responsibility does he have for the murder of his colleagues? How far should undercover officers go to remain undetected?
In real life there were police officers who infiltrated subversive organisations and in some cases formed long term relationships with the unsuspecting members. Marriage and children the outcome of their protracted undercover operations.
Paramilitary organisations have been infiltrated or their members turned by the state in order to undermine their activities and gain intelligence. There is evidence that some murders were allowed to go ahead despite knowledge of the plan to carry out the killings being passed on to branches of the police or MI5. Who makes those decisions and how far should the state go to protect undercover operations? It’s a dirty business.