I think the documentary that Bookchin was referring to is this one. It looks like it was a Granada-MPI Home Video production. I'm not sure where the BBC came into this - unless it aired on BBC originally.

It was a six part series. According to the catalog record for the video, the parts are:
Prelude to tragedy, 1931-6
Revolution, counter-revolution and terror
Battleground for idealists
Franco and the Nationalists
The revolution
Victory and defeat

The video is available is many libraries throughout the country. You can see local holdings here. Enter your zip code to find a library near you.