Learning about the real corruption-busting cops is far more entertaining than Line of Duty

Almost 10 million people tuned in to the latest episode of Line of Duty, the fictional saga about bent coppers with a plot so confusing that some critics have been printing an explanatory guide.

However, to see how the complicated relationship between police and criminals works in the real world, watch Bent Coppers: Crossing the Line of Duty, an excellent new BBC Two documentary series.

Using old footage, brilliant graphics and atmospheric music (with narration by Philip Glenister from Life on Mars), it focuses on the parlous state of the Metropolitan Police in the late 1960s and early 1970s, when a detective was recorded telling a small-time criminal that he had “friends everywhere”.

Bribery was widespread, with one Soho pornographer paying out over £53,000 in just one year – and taking one high-ranking officer on holiday to Spain! After The Times was approached by a crook who claimed he was being blackmailed by officers at Scotland Yard, two journalists launched an investigation that was published in November 1969 and caused outrage.

Further revelations led to Sir Robert Mark forming A10, the Met’s first anti-corruption unit, a week after he had been appointed chief commissioner.

Bent Coppers shows the arrogance of those who proudly claimed that “a firm operated within the firm”, from the Flying Squad to the Obscene Publications Unit, which tipped Soho’s porn shops off before a raid in return for large sums of protection money.

Mark – said to be the inspiration for Line of Duty’s Ted Hastings – eventually sacked 500 officers. Like Hastings, he had a great line in catchphrases, declaring: “A good police force is one that catches more crooks than it employs.”