It starred Edward Woodward as David Callan, an agent of a state secret service dealing with internal security threats to the United Kingdom.

Though portrayed as having responsibilities similar to those of the real-life MI5, Callan's fictional "Section" has carte blanche to use the most ruthless of methods.

Despite being an assassin who stays in the socially isolating job because it is the only thing at which he is good, Callan is a sympathetic character by comparison to his often-sadistic upper-class colleagues and implacable superiors.

The downbeat cover for the Section's headquarters was a scrap-metal business in a former school, belonging to "Charlie Hunter"—an alias inherited by each of Callan’s superiors.

The series pilot episode aired in February 1967, in an Armchair Theatre play entitled A Magnum for Schneider by James Mitchell.

The haunted character of Callan caught the public's imagination to such an extent that a six-episode series was commissioned and broadcast, later in the same year.

The closing episode of the 1969 series saw a severely under-pressure Callan get shot, with a clever publicity campaign following to ensure that viewers cared whether the character lived (he did) or died.

These were supplemented by a 1974 colour film re-working of the pilot, A Magnum for Schneider, .and a 1981 feature-length TV movie, Wet Job.

The Section considered him vulnerable, volatile and dangerous, so had laid him off to a dead-end book-keeping job with an ungrateful employer.

Callan's underworld contact, Lonely (Russell Hunter), developed into an unofficial sidekick, whose shadowing qualities outshone his sense of personal hygiene, something Meres in particular took joy in pointing out.

This run ended with "Death of a Hunter", in which the Section chief meets his demise, and Callan is shot – perhaps fatally.

In the end, Thames decided to bring the programme back in 1970, this time in colour, for a series consisting of a further nine episodes.

In league with Meres' younger, brasher, edgier and unpredictable replacement, James Cross (played by Patrick Mower), the new Hunter concocts a scenario whereby Callan's energies are incited into real emotions that can be turned against the enemy.

However, this move by his masters has motives, and he is eventually relieved of his duties after an incident in which he re-enters the fray as an agent, which was against the rules.

Additionally the DVD includes a new transfer of A Magnum for Schneider and The Good Ones Are All Dead, a music-themed TV special The Edward Woodward Hour, and a documentary on James Mitchell, A World of My Own.

[5] The cinema film was an expanded re-working of James Mitchell's original 1967 TV pilot episode, A Magnum for Schneider.

In the film, Callan's boss Hunter is played by Eric Porter, and Meres too is re-cast, this time played by Peter Egan (known at the time as a trendy gangster, from the controversial TV series Big Breadwinner Hog, but now better known for sitcoms such as the BBC's Ever Decreasing Circles).

The only recurring actors from the TV series were Edward Woodward as Callan, Russell Hunter as Lonely, and Clifford Rose as Dr Snell (who appears in five of the television episodes from series two, three and four, although, in the film, reflecting the screenplay's 1967 origin, it's stated that Callan has never met Snell before).

The tales have been adapted by Peter Mitchell, the series creator's son, and star Ben Miles in the title role, with Frank Skinner as Lonely, Nicholas Briggs as Hunter and Jane Slavin as Liz.

[8] The following is a table listing the awards and nominations received by Callan[9] The series' theme tune, "Girl in the Dark" (also known as "This Man Alone"), was a library piece credited to Dutch composer Jan Stoeckart (under the penname "Jack Trombey", one of several aliases he used), issued by De Wolfe Music.

[10] However, an edition of Billboard newspaper dated 15 November 1975[11] reported on the conclusion of a seven-year copyright case brought in 1968 by Mood Music (a subsidiary of the Sparta-Florida Music Group), who claimed that "Girl in the Dark" was "sufficiently similar" to an Italian song, "Sogno Nostalgico", as to be an infringement of copyright.

Due to the ongoing legal action, the 1974 feature film conspicuously did not use the composition " Girl in the Dark", and the terms of the settlement of the case in 1975 led to its also not being used in ATV's 1981 reunion TV movie.