"We've now got to a micro level with Star Wars, which just isn't interesting any more," he claims. Nor did he want to make something praising or trashing the movie. "We wanted to question the effect Star Wars has had in modern culture through these people's lives. So I had to divorce myself from it as a fan, and even question my relationship to it."
The project was triggered by John Chapman, a student in one of Spira's screen-writing classes. One evening, Chapman mentioned that he'd been in Star Wars. "He took me to his car," Spira recalls, "and opened its boot and, in it, he had these boxes of 10 x 8 photos of himself as an X-wing pilot."
The shot was taken by the on-set stills photographer and when Spira tried to match it to the same scene in the film, he discovered that Lucas had used a different angle and all you could see of Chapman was the back of his head. Nonetheless, he was still able to travel the world selling signed photos of himself.
Spira was fascinated by the "bizarre" psychology that made people buy the photos. Mostly, though, he was interested in what it did to people like Chapman. Did it enrich or complicate their lives?
To find out, he interviewed people who had worked on the film as extras, or in minor roles, including a woman who'd made regular appearances dancing on Ready, Steady Go; a man who played the Stormtrooper known for bumping his head as he charges through a doorway; an actor-musician who'd inveigled his way into a John Lennon/Yoko Ono bed-in; and someone who has invented a martial arts system called zenswim.
The latter, Derek Lyons, will join Spira at JW3 next week for a screening of the film and a post-screening Q&A. He is funny and open in Elstree 1976 and, along with Dave Prowse, who appeared as Darth Vader, illustrates what Spira calls the duality of the Star Wars experience.
Lyons says interacting with fans at conventions (revealed to be potential hotbeds of jealousy, rancour, and humiliation) has helped him to cope with depression. However, Spira suggests that his involvement with Star Wars, which has dominated Lyons' life, has "also, probably, fuelled his depression.
"I think there's a very strange sadness associated with being involved in something massive but knowing that your contribution was not a significant one. And I think they all live with that to some degree."
Prowse, arguably, embodies this more than anyone.
"[The interview] started off very friendly and jocular and then it just got darker and darker," says Spira. "I wanted to keep that chronology in the film. I wanted it to feel the way it actually felt in the room. When you first meet Dave, you just think he's this lovely old man and after a while you realise there is a real darkness, there's a real bitterness, and it's highly questionable, for him in particular, how good the Star Wars experience has been."
Prowse is proprietorial over Darth Vader, the most famous character in the Star Wars canon. In truth, though, the role was played by at least three people, says Spira, including James Earl Jones, who overdubbed Prowse's dialogue.
"I've certainly heard from various places that George's take on Dave is a confused one, because for him he was always just the guy doing the walking and the pointing."
Ultimately, Spira isn't sure how good Star Wars has been for any of the people interviewed. His previous documentary, Anyone Can Play Guitar, about the Oxford music scene, was a "diatribe" certain of its message. Elstree 1976 reflects more his contention that there is "no such thing as truth, there is only perspective".
Raised in an Orthodox Jewish family, Spira says he's recently been thinking about how this has informed his film-making. He was the only Jew at his school in Oxford, he says, and "felt like I was the little Jewish guy in a Christian/Waspy society. I was respectful and enjoyed those communities, but didn't feel a part of that." In his work, this has translated into a focus on communities - musicians, actors, and in his next documentary, Funny Bones, comedians - "which I have an affection for, but which I very much feel on the outside of."
Spira adds: "The other thing you have to remember about Jewish creative people in particular, is that ours is a religion and a culture that is based on questioning… Usually, I think, when you're brought up religious, it can be quite an indoctrination thing. You're told how to think. Whereas being brought up Jewish, it's the opposite: you're taught how to question and that you can still love something while questioning it. So I think that also informs everything I do in terms off documentary."
In 2013, he wrote an article about how John Landis's American Werewolf in London is one of the great Jewish films. When he saw it as a child, a dream sequence in which a Jewish family not unlike his own is massacred by demonic Nazis evoked a feeling of primal terror. Years later, he decided that it had tapped into the fear at the heart of post-Holocaust Judaism: that "the idea you can build a comfortable home in a country is tenuous at best".
This is something that's very much on his mind in the current political climate.
When you first learn about the Holocaust, he says, "there is a period of re-examining who you are and how you fit into society, and we're at one of those points again in the world, where it can become a real possibility."
The real world is a lot less simplistic than George Lucas's Manichean fantasy.
But the hope, nevertheless, must be that the forces of light will ultimately hold back the darkness descending over it.
