BY 1967, WITH THE COLD WAR at its most deeply frozen and Sean Connery’s Bond prowling movie screens, the public’s love affair with the world of espionage was at its height. The success of the 007 franchise had inspired an explosion of spy movies and television series, many simply trying to ape the Ian Fleming formula – but the most interesting amplifying upon, or kicking hard against it. Of the latter, Callan, which debuted on British TV that year to lay out the astonishingly downbeat adventures of a lowly, self-loathing state assassin, represented the very end of the line.

Played to the hilt by the late Edward Woodward, David Callan was the spy who hated his bosses and his job. In his seedy world, assassination was not an exciting, globetrotting occupation with plenty of perks. Rather, it was grubby, soul-destroying menial work. He remains the most believable spook we’ve ever had. There had been haunted and conflicted secret agent loners before, of course, and there have been countless since – Jason Bourne is only the latest manifestation – but none have really gone further, or got deeper down into it.

The Bond movies’ globe-trotting Technicolor glamour, military-industrial gadgetry fetish and increasingly tongue-in-cheek sense of fun had a seismic impact on the development of the UK’s small-screen spies. Taking cues from 007, running with and subverting them, The Avengers evolved from a cheap, shadowy thriller into a bright, hard, sublimely strange modernist-surrealist Pop fantasy, the mood of which Patrick McGoohan would subsequently twist toward paranoid nightmare with his own berserk masterpiece of 1967, The Prisoner.

Callan, however, looked to another model: not Bond, but the nameless protagonist of Len Deighton’s chillier, more ambivalent spy novels, the character Michael Caine brought to the screen as Harry Palmer in 1965’s The Ipcress File. The Palmer figure lived a smaller, shabbier life than 007 and he made spying seem more a humdrum, thankless job. But if Deighton’s anti-hero was, as critics dubbed him, “the Kitchen-Sink Bond,” David Callan was something else again. A sullen, resentful, presence, as distrustful of his own superiors as the enemy, and stuck in a twilight world of grinding sleaziness, he was the Bond from beneath the kitchen sink: a damp, dank, dark place, where the work is cold, wet and dirty, and everything stinks. The show’s mood was set by its title sequence: a bare lightbulb swinging on a wire in a brick basement, while a hesitant tune suggests John Barry’s Ipcress File theme sunk into a suicidal depression. (Callan‘s excellent theme music was a library piece originally titled “Girl In The Dark,” composed by Jan Stoeckart, better known under his pseudonym Jack Trombey, who also wrote the similarly brilliant – though otherwise utterly dissimilar – “Eye Level,” aka the theme from Van Der Valk.)

Written by James Mitchell, a sometimes Avengers contributor who would go on to create another working class hero in When The Boat Comes In, David Callan first appeared in a one-off play, A Magnum For Schneider, part of ITV’s celebrated Armchair Theatre strand. Employed by a nameless government agency known as “The Section,” he’s a highly proficient operative, but he has all the status of a janitor.

Overseen by a figure called Hunter (a codename, it becomes clear: as with The Prisoner and its “Number 2,” Callan faces off against a succession of individuals with the title), The Section specialises in removing individuals considered too dangerous to remain at large, sometimes by “persuading” them through frame-ups and blackmail, often by killing them, the “wet jobs” at which Callan excels.

One of TV’s first great fuck-ups, Callan has a conscience, but is often a fairly unpleasant individual. The closest he has to a friend is his informant, Lonely (played with a sublime, crumbling touch by Russell Hunter), a Gollum-like bottom rung criminal and alcoholic, further blessed with severe hygiene issues. Lonely considers Callan his pal, anyway, even though the spy frequently threatens to beat him, apparently just for the pleasure of seeing him cringe. We’re a long way from Steed and Mrs Peel here. All Callan’s relationships are perverse. His association with Lonely runs on melancholy sadism. His hatred of his employers and colleagues borders on psychotic. Time and again, the person he comes closest to developing a kinship with is the person he’s tasked to kill.

Somewhere along the line, though, something has gone wrong – or gone right – inside him. Instead of just getting on with his job and following orders, he started questioning them, worrying over who his victims were, what exactly they had done, whether they deserved to die. As Mitchell’s drama begins, Callan, has, in another parallel with The Prisoner, already gone through a breakdown of sorts, and resigned in disgust.

Rather than being whisked off to an exciting and mysterious prison Village, however, his old employers come up with a more prosaic fate for him. Keeping him on a short leash, they’ve set him up with a crushing dead-end job, working as a bookkeeper for a shabby little business in a shabby little office, under a shabby little man he loathes, earning just enough to be able to afford to rent a squalid bedsit. As much as he hated his work for The Section, however, it seems he hates the routine of this straight life even more, and, when Hunter finally offers him a chance to come back, carrying out another under-the-radar execution, he reluctantly returns to the fold. And then, as the dirty old game of deceit, murder, guilt and treachery gets underway again, quickly remembers why he quit.

As played by Woodward, the figure of Callan instantly captured the audience’s imagination and, following the play’s transmission, a full series was commissioned. Callan ran for four series between 1967 and 1972 but, until now, its cult status has rested largely on the last two series, shot in colour, which have been kept relatively easy to see through repeats and video releases.

Unseen since their initial broadcast, however, the original black-and-white series have never been released before – in part because they no longer fully exist. Having fallen prey to the barbarous habit of tape-wiping that has blighted the UK’s Golden Age TV archives, only two programmes from the first batch of six programmes remain, and six of the 15-episode second series are seemingly gone for good.

Finally compiling what survives – the pilot play, plus eleven episodes – a new, long overdue box set, Callan: The Monochrome Years, is a godsend for fans, and, while frustratingly fragmented, it is something of a revelation. After living with those brilliant colour episodes for years, it’s strange to go back and realise Callan’s most compelling storyline actually came before. Without giving much away, Series Two builds to climax with an episode entitled “Death of a Hunter.”

Other titles here ably suggest the atmosphere of this show: “The Good Ones Are All Dead”; “Let’s Kill Everybody”; “Nice People Die At Home.” Things develop from episode to episode, but, in a sense, the basic plot of “A Magnum For Schneider” keeps repeating: Callan gets called upon to kill, argues with his boss, wrestles violently with his own humanity, and usually winds up killing anyway, because there’s not much else he can do, nowhere else he can go.

The sense of repetition though, combined with the stark, bare, airless shooting style engendered by the low budgets, only helps heighten Callan’s uniquely intense atmosphere of entrapment and claustrophobia. These sets might be flimsy, but the writing and performances are resoundingly tough. Cherished though his sterling work in The Wicker Man might be, Woodward really was never this good. A contemptuous, working class anti-hero, he’s far looser, and far more tightly reined in here than you will see him anywhere else. His delicately nasty scenes with Hunter as their deeply perverse relationship plays are out a particular delight. For fans, this box set offers an experience akin to The Wizard Of Oz in reverse. Passing from colour back into the black and white world, you realise that Callan only ever really existed in endless shades of grey.

A version of this review ran in Uncut, January 2010