In Seventies London it’s the age of the supergrass – and the men who ran them. Supergrass tells the story of a decade when coppers got too close to criminals, and of a crime-busting system that seemed too good to be true.

Like a true Life On Mars, with first-hand insight from the major players, Supergrass illuminates a world that seems a million miles away, yet is near history. In a compelling mix of drama and testimony, this 90-minute, action-packed crime story runs through one of Britain’s most violent decades.

The supergrass system provided the key to cracking down on armed robbery when gangs ran amok in the streets of the capital, but it also carried a terrible risk. When coppers began to believe informers without question, the system was bound to collapse and leave the Metropolitan Police in chaos.

Britain’s first supergrass, Bertie Smalls, was a seasoned armed robber and gang leader. His evidence led to the arrest and conviction of dozens of associates and hundreds of years in sentences.

His deal, with absolute immunity from conviction, was never to be repeated as the Law Lords acted to prevent others getting away scot-free. But this didn’t stop villains such as Maurice O’Mahoney, one of Britain’s most violent armed robbers, negotiating their own deals. With a bounty on his head, O’Mahoney turned in more than 150 names in exchange for a much-reduced sentence.

During this period, one police officer emerged as the “supergrass master”, running the system from Finchley nick. Tony Lundy, who speaks out after many years of silence, was better at running the grasses than anyone else. Lundy tells how he was caught up in a campaign of allegations and agendas within the Met and the criminal fraternity. Never found to be corrupt, and proud of his record, Lundy was criticised for having too cosy a relationship with those he was trying to convict.

This is policing in classic Sweeney London where no one quite knew what the rules were.