Twenty years ago this June, a series described by its creator, David Simon, as a “novel for television”, premiered on HBO in the US. Simon had shrewdly pitched The Wire to the cable network as a cop show; its title refers to the use of electronic surveillance to catch drug dealers. His writing partner, Ed Burns, was an ex-Baltimore cop; Simon had worked for the Baltimore Sun as a police reporter. They knew their subject.

But The Wire is more than a police procedural. In 60 episodes over five series, it lays bare the limitations of Baltimore’s institutions: City Hall; the police department; the education system; the dockers’ union; and the local newspaper. Both Simon and Burns had much to say about the city’s endemic drug crime and the racism, corruption and poverty that fuelled it.

The thread that runs through this discourse on a malfunctioning city is the age-old cops and robbers’ story; in this case, the Baltimore Police’s attempt to bring the city’s drug dealers – and the Barksdale empire in particular – to justice.

It took mainstream British audiences until March 2009 (FX channel had earlier broadcast it to tiny audiences) to discover what the fuss was about – by which time, the series had ended in the US. When they did, despite BBC Two’s late-night scheduling of the show and its unavailability on iPlayer, viewers embraced it.

There were a few surprises. The Wire had a predominately black cast, almost unheard of two decades ago, but one that accurately reflected Baltimore’s population. Among the unknowns and barely knowns were real-life Baltimore figures – including ex-cons – and a surprising number of actors from this side of the pond.

Dominic West, in his first major role, played a wayward Irish-American cop, Jimmy McNulty; the more established Aidan Gillen was local politician Tommy Carcetti; and Idris Elba, Stringer Bell, was a gang boss trying to legitimise his business.

A couple of years ago I interviewed Elba, who had moved to the US around the turn of the millennium to find meatier roles than he ones he’d had in The Bill or Silent Witness. He recalled: “I was absolutely broke. It was time to pack up and come home. But luckily The Wire came along.” His accent was note perfect. During the auditions Simon failed to spot his East London inflection.

The villains and the dispossessed were as central to the series as the cops. Stick-up man Omar Little, played by the late Michael K Williams, specialised in robbing dealers. No less a figure than Barack Obama was just one of many viewers drawn to him: “He’s a fascinating character – a gay gangster who only robs drug dealers, and then gives back, sort of a Robin Hood. And he’s the toughest, baddest guy on the show.”

Homeless heroin addict and police snitch Bubbles, played by Andre Royo, was another who added to the humanity of a show that always gave the downtrodden dignity.

Audiences for The Wire on HBO were disappointing, perhaps put off by the show’s languid pacing and complex plot, or maybe Simon’s extravagant ambition. “Our model when we started doing The Wire wasn’t other television shows. The standard we were looking at was Balzac’s Paris or Dickens’s London, or Tolstoy’s Moscow,” he once said.

Simon has suggested that a largely black cast and heavy use of slang could have limited its mass audience appeal but, as Royo noted, “For the [black] middle-class and the urban communities – this is our story. This is our Sopranos, this is our Six Feet Under.”

Awards were also thin on the ground. The series never won a Primetime Emmy. Critics, though, embraced it from day one. And, last year, in a BBC poll of 200-plus TV experts from 43 different countries, The Wire emerged as the clear winner – the greatest TV series of the 21st century.

The Wire is available on Amazon Prime Video and Now TV.