The original crew of Blake's 7: from left-to-right, thief Vila Restal (Michael Keating), telepathic guerrilla Cally (Jan Chappell), freedom fighter Roj Blake (Gareth Thomas), pilot Jenna Stannis (Sally Knyvette), computer genius Kerr Avon (Paul Darrow) and idealistic fighter Olag Gan (David Jackson). The seventh character is the Liberator's powerful AI, Zen (Peter Tuddenham).
Engineer Roj Blake had previously led a failed rebellion against the government. He'd been captured, brainwashed and turned into a model citizen to show the futility of rebelling against the state. However, his former allies "rescued" him, restored his sense of justice and heroism and started planning a second rebellion. This was crushed in its infancy and Blake was exiled to the prison planet Cygnus Alpha. Along the way he escaped with the help of his criminal shipmates and an derelicted alien starship they discovered along the way. Using this ship, the Liberator, Blake planned to wage war against the Federation to destroy it. His more selfishly-inclined criminal shipmates, however, often had other ideas on how to use their good fortune.
The result was an incredibly bleak and unceasingly cynical TV show, very much at odds with the boo-yar optimism of most contemporary space opera. Blake's crew were often defeated or forced into morally complex situation where Blake's simplistic view of good and evil was hopelessly compromised. The show was rooted in the conflict between idealism and pragmatism and writers like Nation and Chris Boucher mined this conflict to great effect.
The show had rich, endlessly-quotable dialogue, fine performances (particularly from Gareth Thomas as Blake and Paul Darrow as his amoral, aloof foil, Kerr Avon) and quite astonishingly bad production values, even for 1978. The producers organised a trip to see the first Star Wars movie - which wasn't released in the UK until January 1978 - and were horrified at its effects, feeling that their show couldn't help but look dated in comparison. Fortunately British audiences responded to the show and it eventually ran for a respectable four seasons and 52 episodes, ending in 1981 with a famously dark ending where almost the entire regular and recurring cast is brutally gunned down by Federation troopers.
There have been attempts to remake the show from time to time, often by writers whom it sounds like had very little understanding of the show and its rich, complex ideas. More successful were writers inspired by Blake's 7: J. Michael Straczynski was a big fan of the show and used some of its structural ideas in Babylon 5. A young Joss Whedon watched the show whilst at boarding school in England, and it's DNA and fingerprints can clearly be found in his later space opera Firefly.
Blake's 7 also pioneered the use of the big season-ending cliffhanger, with each season ending with a huge, shocking event which ensured audiences would return next season. It would be another twelve years before American SF cottoned on with Star Trek: The Next Generation's Best of Both Worlds season-ending event.
Happy anniversary to this classic show, and here's hoping that if it is remade, it's done by someone who has a good handle on the source material.