A corrupt police officer pulling the strings like 'H' in Line of Duty is the stuff of nightmares.
But the dark fictional storyline is actually based on a sinister real-life network of corruption within the police which went all the way to the top.
The high-ranking officer believed to be the inspiration for the character of 'H' in Line of Duty escaped justice, but could give us some vital clues as to how the dramatic series finale will end.
Masonic dealings, brown envelopes with bribe money are secret recordings are all things we've seen AC-12 investigate, but they all actually happened in real-life.
Back in the 1970s when London was under threat from drugs, pornography and violent robbery, bent coppers were operating with impunity, becoming known as the 'firm within a firm'.
"People were getting arrested but they were getting bail and the evidence against them appeared to be getting watered down. Rumours began to circulate that deals of some sort had been done," explains investigative journalist Martin Short.
BBC documentary Bent Coppers: Crossing the Line of Duty looks at how three major armed robberies were covered up by bent coppers giving out bribes, planting evidence and the supergrasses and whistleblowers who exposed them.
With serious allegations linking pay offs from criminals to corrupt officers coming out, the government were forced to act and brought in an outside force to investigate the City of London Police.
Operation Countryman saw officers initially from Dorset and then other regional forces looking into claims that City of London Police officers were bent.
Criminals had become sick of the greed of police officers and were giving credible evidence against them, but they needed the testimony of whistleblowers to prove it was true.
Some corrupt officers were offered reduced sentence for testifying against their colleagues and became known as 'supergrasses'.
Former DC Lew Tassell of the City of London Police describes being handed £50 notes by his commanding officer DCI Phil Cuthbert.
"It was expected of me to accept it. It was part of the culture and I should be grateful for it. I never considered giving it back," admits Tassell.
Being given money in a brown enveloped was referred to as "taking a drink" and officers would suddenly become corrupt without even realising the significance.
Tassell says the higher up the chain you went the bigger the 'drink' and there was no one he could report the bribery to.
Eventually while being investigated he decided to come clean but he was terrified of the consequences, fearing not only for his future in the police but for his life.
"There's an unwritten rule in the police, you’re supposed to keep your mouth shut. If you go to someone and make and allegation you're effectively a whistleblower," says Tassell.
He was particularly concerned for his own safety when an officer accused him of being a grass, then another replied: "No I don’t think he's a grass because if what you say is true you'll be wearing a cement raincoat."
Terrified Tassell admits he would sometimes go home and sob, but he bravely faced Cuthbert in the witness box and he himself was never charged with taking bribe money.
Cuthbert went to trial at the Old Bailey and was given a three-year prison sentence for conspiracy to obtain bribes and corruptly presenting evidence - but he was not believed to be the highest ranking bent copper.
DCI John Simmonds, who previously served with A10, the anti-corruption department of the Met which the fictional AC-12 in Line of Duty is based on, uncovered some startling evidence. when he was appointed as the new head of CID.
Cuthbert and Simmonds were both active Freemasons and the bent copper wanted to speak "on the square", which means off the record due to the oaths they had taken.
Cuthbert told Simmonds that the person at the top of the corruption pyramid was Commander Hugh Moore, who was the third highest ranking officer in the City of London police.
Discussing Cuthbert's confession, he says: "I think he was panicking having been told by Hugh Moore that this big inquiry was going to go down and Cuthbert was going to be on his own and be the fall guy, the man blamed for all that had gone on."
Cuthbert thought that the Masonic bond would be so strong that Simmonds would turn a blind eye, but he kept Freemasonry and his role in the force separate.
"When he started admitting to criminality I withdrew by Freemasons hat and put my police helmet back on as I realised this was exceedingly serious," admits Simmonds.
"Cuthbert assumed I was on his side and would back him in the event of him coming unstuck but it was my word against Cuthbert so there was a need to corroborate what was being said."
In 1976, four men in wigs and glasses burst into the Daily Express offices and stole the £175,000 payroll, but when an officer found a van with money bags and shotgun cartridges he was adamantly told it was not the getaway vehicle.
The following year in September 1977, a security van was attacked while delivering £520,000 to Williams & Glyn’s bank and the driver was shot in the leg.
Six suspects were charged in connection with the bank job but they were released one by one, then went to court and were bailed despite being dangerous criminals and posing risk to public.
"Someone had been shot. How did you get bail on something as serious as that? That is really ringing the alarm bells," says John O’Connor, CDR Met Police.
A security guard was also killed during Daily Mirror payroll robbery in May 1978, where the attackers managed to escape with £200,000.
City of London firearms officers were supposed to be patrolling the area but had been forced to attend a 'scenes of crime' lecture given by Commander Hugh Moore.
Inspector Derek Smith claims it was "very odd" this event was taking place for the first time and Moore was handed a note during the lecture.
Smith says Moore looked up at one of the "snarking" officers near him then revealed there had been an armed robbery at the Daily Mirror building, adding: "Our sergeant kicked a chair towards the Commander and he just laughed at us."
In total, eight men were arrested in connection with the three armed robberies and all charges against them were dropped.
Simmonds was fitted with a microphone and got Cuthbert on tape revealing more than £20,000 had been handed to police over one of the armed robberies, which is worth more than £100,000 now.
Moore was never prosecuted and denied the allegations made against him by on a secret tape by Cuthbert, who then claimed he was drunk at the time and did not name any other corrupt officers.
Simmonds has stated his belief that Moore was "bent and crooked" and could have been the inspiration for 'H', the fictional corrupt officer pulling the strings at the top in Line of Duty.
He claims he was given a hard time by Moore daily, who made snipes and tried to trip him up, so he became disillusioned with the police and retired in 1982 after 27 years in the force.
Moore continued as Commander for another 10 years before he died of heart failure while attempting an arrest.
After four years Operation Countryman was wound down and out of 200 allegations investigated, no Met Police officers were convicted of any offences.
*Bent Coppers: Crossing the Line of Duty airs Wednesdays on BBC Two at 9pm
