It is hard now to convey the shocking originality of Cracker, the 1990s ITV crime series that helped redefine the genre and bring some genuine unpredictability and real edge to Monday-­night, peak-time TV.

At a stroke, Cracker made a star of man mountain Robbie Coltrane, previously known for his work in lighter fare such as the BBC Two series Tutti Frutti, in which he plays the singer in a Scottish rock ’n’ roll band alongside Emma Thompson and Richard Wilson.

To see this erstwhile comic actor become the scene-stealing, deeply flawed forensic psychologist, Dr Edward Fitzgerald – Fitz to his friends – was truly a revelation. Incredibly, Cracker’s creator, the brilliant Jimmy McGovern, had originally envisaged his anti-hero as a wiry man like himself. He was overruled by the casting director and vowed never again to be involved in a casting decision.

Cracker, one of Granada’s brightest crown jewels, was the antidote to Miss Marple, The Ruth Rendell Mysteries and all those other genteel Home Counties murder mysteries that provide succour rather than sensation. The series’ antecedents perhaps go back to Z Cars, another gritty, blue-collar Northern crime show that broke down taboos and stereotypes in relation to the portrayal of fictional law enforcers on TV.

McGovern acknowledged that part of his inspiration for writing Cracker was the long-running American police show Columbo, whose eponymous central character was, like Fitz, a thoroughgoing slob. In one famous scene, Coltrane impersonates Columbo, who was played by Peter Falk.

From the opening sequence of the first episode, initially broadcast in 1993, we know that Fitz is a gambler and a maverick. Lecturing to a group of ­psychology undergraduates, he hurls at them a succession of books written by famous western thinkers whose speciality was the human condition.

“Spinoza, Descartes, Hobbes,” Fitz snarls as each tome is thrown into the body of the lecture theatre. “Locke… Freud.” The message is clear; if you really want to learn about human behaviour, then take a close look at the dark heart that beats within us all.

“Go and lock yourself in a room for a couple of days, and study what is here,” advises Fitz, tapping his heart. “The things that you really feel, not all that crap that you’re supposed to feel. And when you’ve studied, when you’ve shed a little light on the dark recesses of your soul, that’s the time to pick up a book.”

The inference is that one reason Fitz is so valuable in helping the Manchester police to solve their most challenging and vile murders is because of his own self-knowledge that “there but for the grace of God go I”. Not for nothing was McGovern raised a Catholic.

“I drink too much, I smoke too much, I gamble too much, I am too much,” Fitz declares, but it’s his thinking approach to solving crimes that deliver results that elude conventional police investigation. Not that Fitz doesn’t make mistakes, too.

“You’re an emotional rapist,” DS Jane Penhaligon (Geraldine Somerville) tells him in one of Cracker’s most famous episodes, To Be a Somebody, in which their boss, DCI David Bilborough (Christopher Eccleston), is himself murdered.

Fitz is an unlikely sex symbol but, over the course of Cracker’s three seasons, Fitz and Penhaligon pursue an unlikely love affair, while his marriage to the very long-suffering Judith (Barbara Flynn) crumbles, partly due to his alcoholism and gambling.

In common with so many other great shows, Cracker was something of an academy for future small- and big-screen talent. An early director on the series was Michael Winterbottom. Nicola Shindler worked as a script editor on Cracker before setting up Red, one of the 21st century’s most successful independent producers of scripted content.

Granada was thrilled when the US agreed to adapt Cracker, but, across the Atlantic, Cracker was a commercial and artistic flop. However, in the context of US TV, it is worth noting the verdict of Den of Geek on what is unquestionably a groundbreaking British series: “It shows the world that the UK was capable of out-HBOing HBO even before HBO existed.” Too true.

Cracker is available on ITV Hub and Amazon Prime.