On Friday, Citizenfour, a documentary about Edward Snowden and his revelations of the mass surveillance operations of the US, UK and other governments, had its British premiere in London. The 114-minute film had its world premiere at the New York Film Festival on October 10.

Citizenfour is directed by Laura Poitras, the award-winning American documentary filmmaker. Poitras was the first individual Snowden contacted about his devastating revelations and to whom he made available his archive of National Security Agency (NSA) documents. The documentary was filmed by Poitras, Kirsten Johnson, Katy Scoggin and Trevor Paglen. Filmmaker Steven Soderbergh is one of three executive producers.

The UK premiere was part of the British Film Institute’s (BFI) 58th London Film Festival. Citizenfour was presented as a Documentary Special, screened to a packed house at London’s Curzon Chelsea and again on October 18 in the capital’s Hackney Picturehouse. The Curzon screening was followed by a question-and-answer session with Poitras via Skype from Berlin, Germany where she resides. Citizenfour and the Q&A were simultaneously screened in 70 cinemas nationwide, in all of the UK’s main towns and cities.

During the question-and-answer sessions, Poitras explained that Citizenfour was the last part of a “9/11 trilogy”; the previous films being My Country, My Country and The Oath. In January 2013, while Poitras was in the process of making a film about abuses of democratic rights in the US following 9/11, she began to receive encrypted e-mails from Snowden who initially identified himself only as “Citizenfour”.

The film recounts how, in one of his first e-mails to Poitras, Snowden informs her “for now know that every border you cross, every purchase you make, every call you dial, every cell phone tower you pass, friend you keep, site you visit, and subject line you type is in the hands of a system, whose reach is unlimited but whose safeguards are not.”

He adds, “In the end if you publish the source material, I will likely be immediately implicated. I ask only that you ensure that this information makes it home to the American public.”

In late May 2013, Poitras, then Guardian journalist Glenn Greenwald and another Guardian reporter, Ewen MacAskill, travelled to Hong Kong to meet Snowden. Poitras recorded the Guardian interview in a hotel room in Hong Kong in which Snowden revealed his identity.

The film documents this experience and includes fascinating new footage and interviews with Snowden shot in the hotel room. He, Poitras, and the Guardian journalists discuss the material he is in possession of and the urgent necessity of making it available to the world’s population.

Citizenfour brilliantly captures the tensions and anxieties of all concerned in the hours and days that followed the material being made public, and as Snowden’s fate hung in the balance with the imminent threat of his seizure and incarceration by US security/intelligence forces. Moving scenes show Snowden’s great concern as to the impact his actions are having on his family and his girlfriend in the US, as he learns she is undergoing interrogation at the hands of the American government.

Snowden says at one point, “We are building the biggest weapon for oppression in the history of mankind.”

The fate of Poitras herself and the other journalists involved reveals the extent to which this onslaught against civil liberties has grown in the 18 months since the publication of Snowden’s documents.

In response to a question as to the reason for her not being able to attend the London screening, the documentary maker explained that her absence was “[B]ecause of the laws of the UK, the UK Terrorism Act, and also the Official Secrets laws that make publishing this kind of work very dangerous for journalists. As you see in the film, Glenn’s partner David Miranda was detained for many hours and I’ve just been advised by my lawyers, ‘Just don’t go to the UK,’ so that’s why I’m not there.”

The director personally thanked others involved in the film who also could not be at the showing on the advice of lawyers, stating “First and foremost I’d like to thank Sarah Harrison [WikiLeaks Legal Defence representative] and Julian Assange [WikiLeaks founder] who can’t be there. As you know it was their effort that secured political asylum for Edward Snowden and they deserve enormous credit for that.”

The London audience cheered and applauded Harrison and Assange, as well as those WikiLeaks representatives in the audience.

Poitras also thanked Trevor Paglen, who was able to attend the event and fielded some questions, stating that he was “the extraordinary photographer who did the images of the [UK government] surveillance sites that you see at Bude and Menwith Hill station.”

Explaining how Citizenfour came to be made, she commented, “In 2004 I made a film about the war in Iraq not knowing that it would be a series of films. I thought maybe the US would take a different course. I didn’t think we would still be moving down the path we are. After that, I was still editing and I was shocked that Guantanamo [Bay prison] was still open; this was in the summer of 2005. I thought I had to make a film about Guantanamo because this really is a national shame that this is still open, so I made a film called The Oath.

“When I was working on that, that’s when I knew this was going to be a series of films and I wanted the final part to take the story home and domestic surveillance was one of the first things that [President George W.] Bush did after 9/11. They issued the Authorisation for the Use of Military Force and then they rolled in servers to begin domestic spying in the US. … The people who were targeted in the immediate aftermath of 9/11 were Muslim Americans in the US, but then it became wider.”

“On a personal note,” she added, “in 2006 I was put on a watch list and I started being stopped and questioned every time I travelled to the United States, so I became personally aware of the dangers and threats that it posed for everyone, but also in my position as a journalist.”

Citizenfour is being co-distributed in the UK by Artificial Eye and BRITDOC Foundation and will be in UK cinemas from October 31 as a Film4 co-production. The terrestrial UK TV station Channel 4 is to show the film in early 2015.