Just found this:
https://en.wikipedia.org/wiki/Paul_Darrow
Interesting. So he has the rights.
Proud of his work on Blake's 7, Darrow has acted as the show's most prolific spokesman, both in the UK and during the late 80s, in the U.S., when the show was frequently broadcast on US public television. In the mid to late 1990s, he purchased the rights to Blake's 7 and attempted to produce a big-budget follow-up mini-series, Blake's 7: A Rebellion Reborn. According to Darrow, it would have begun 25 years after the ending of the original series and might have included an aged Avon passing the torch to a new generation.
https://en.wikipedia.org/wiki/Paul_Darrow
Interesting. So he has the rights.