Terminal , the final episode of season 3, was originally going to be the end of Blake's 7 (this is why Gareth Thomas was persuaded to reprise the role of Blake for the episode, which of course happened again for the real conclusion).
The destruction of the Liberator was a suitably dark ending to the show, and the real set was used for filming its destruction (March 7th, 1980).
The end was so certain, that when the episode was broadcast (March 31, 1980), the cast and crew had already dispersed.
Most of them didn't even know that there would be more episodes until this was announced during the credit sequence at the end of Terminal .
The story (according to the Blake's 7 Summer Special for the final season) is that the Head of BBC Television was impressed by the episode and instructed (while it was airing!)
that an announcement be made during the end credits that the series would return.
At this point, there were both in-universe (it was a fairly definitive destruction, unlike the destruction of the 'sister ship' in the first season, and this was stolen technology was more advanced than most, so not easily repaired/rebuilt) and out-of-universe (the set was blown up!)
reasons to need a new ship, rather than a repaired/rebuilt Liberator .
Peter Tuddenham voiced both Zen and Slave (the computer of their next ship, Scorpio ), and also Orac, who survived the Liberator 's end.
Since he was already continuing as Orac, it made sense for him to do the voice of the new ship as well (and Zen and Slave's characters were sufficiently different that it wasn't especially obvious that this was the case).
scifi.stackexchange.com/users/108/Tony Meyer
The destruction of the Liberator (in the context of Terminal being the final episode at the time) provided Nation with with the opportunity to give Servalan what she has been seeking for the entire series...but only for a short time.
Servalan's desire for the Liberator can be argued as being the main story arc of Season 3 and this is arguably one of the reasons why many see Season three as weaker than season 1 or 2 as there was no real story arc for the heros.
It is even mentioned on the DVD commentary that when Tarrant says to Vila "Can't always have what we want now Villa...
" that this is the main theme of the episode.
Here we see the obsessed Servalan seizing control, gloriously commanding "maximum power", only to have her whole prize disintegtrate around her.
The destruction of the Liberator therefore becomes one of the strongest symbols of irony in the (entire) series.
Avon's smile at the end is also such a symbol of irony.
Throughout season 1 and 2, Avon had tried frequently hinted that he wanted the Liberator, "I am free, I intend to stay that way", "....
I will take you back to earth
then the Liberator is mine, agreed ?
" even proclaiming "This is MY ship" in Powerplay.
In Terminal, Avon is tricked into believing that Blake is alive, he falls into the trap, based on Servalan's conditioning about Blake.
"You wanted to belive Blake was was alive" and yet, in his persuit of Blake, he looses the one thing that he managed to win from Blake in the first place.....
The destruction of the Liberator therefore provides Ironic tradgedies to both hero and villian and was a stroke of genius from Nation.
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A Blake's 7 magazine of the mid 1990's said that makers were influenced by the film Alien , which they found darker and a more grim reality.
They thought Liberator was too glamorous.
Though some of the Alien films are quite good, Blake's 7 is superior, and should never have sought to copy something inferior.
Best regards.
Steven Summer, of the Blake's 7 obsession website.
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I saw in an interview, it was for one simple reason.
The set was falling apart.
If it was not broke, it was stolen by visitors to set.
Limited wrist bracelet and guns.
So they started over.
scifi.stackexchange.com/users/30516/Joseph Smith
Very simple, everyone associated with the show thought that 'Terminal' would be the final episode of the series.
Therefore, they destroyed the Liberator sets in one massive finale.
scifi.stackexchange.com/users/47156/Roj Blake
I read somewhere that the technology of the federation was catching up with that of the Liberators.
And the new persuit ships that Servalan had nearly caught them in a trap .Not
sure of the episode now, mentions the new persuit ships,so Blakes crew where going to have to upgrade soon anyway,which they got in Stardrive.
The photon drive or Stardrive was fitted into Scorpio.
Which makes sense ,everything is oudated sooner or later.
scifi.stackexchange.com/users/32810/kenobi one
The Liberator was a beautiful ship design with good sets and an interesting computer (Zen). My question is not why it was destroyed in-universe, but why the writers decided to get rid of it. Was it too powerful? Did they have to dismantle the sets for some reason (cost, perhaps)? Did the new producer try to fix things that weren't broken? Did the voice of Zen choose to leave the show?
Why did the writers of Blake's 7 destroy the Liberator?
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Terminal , the final episode of season 3, was originally going to be the end of  Blake's 7. The destruction of the  Liberator  was a suitably dark ending to the show, and the real set was used for filming its destruction (March 7th, 1980). It is also said that the set was falling apart. AS this was supposed to be the final episode of the series the directors wanted to go out with a big bang. In addition it served the plot conveniently as tp give Servalan what she had been seeking, but only for a short time as a cruel twist of irony. In addition there were some rumours about the set falling apart and so they needed to come up with a new one after the show was re-newed.
Terminal was supposed to be the final episode of the series and The Liberator being destroyed was going to be part of the big finally. The destruction of the Liberator served as plot convenience at the end of the season to allow Servalan to take control of the ship she was seeking, but only for a short time allow for a cruel twist of irony. The set was falling apart