Steven Spielberg believes we will discover aliens in our lifetime

For more than 40 years, Steven Spielberg has been asking audiences the same question: what if we're not alone?

From the friendly alien at the heart of E.T. to the mysterious visitors in Close Encounters of the Third Kind, some of his most celebrated films have explored humanity's fascination with life beyond Earth.

Now, the Oscar-winning director is returning to that theme once again with Disclosure Day, a sci-fi thriller starring Emily Blunt, Josh O'Connor, Colman Domingo, Colin Firth and Eve Hewson.

The film imagines a world on the brink of a revelation: proof that non-human intelligence exists and has been hidden in plain sight.

At the centre of the story are Blunt's character, meteorologist Margaret Fairchild, and O'Connor's Daniel Kellner, a cybersecurity expert who uncovers evidence of a long-running cover-up and finds himself pursued as governments and powerful corporations race to contain the truth.

Speaking at the UK premiere in Leicester Square, Spielberg told the BBC he remains captivated by the question that has inspired some of his most iconic work and his view on the possibility of extraterrestrial life has evolved over the decades.

"My view has become more realistic," he said. "There's a lot of mystery and things that are undisclosed but I've become more optimistic that people are going to be able to discover things that we have not been allowed to discover."

The film arrives at a time when discussions about unidentified aerial phenomena, government transparency and artificial intelligence have moved from the fringes of popular culture into mainstream debate.

While Disclosure Day centres on the possibility of extraterrestrial life, many of its themes focus on trust, secrecy and how societies respond when long-held assumptions are challenged.

Most importantly, according to the 79-year-old filmmaker, it centres ultimately on humanity.

"It's about empathy and bringing people together" and an event like discovering the existence of aliens "would bring people together", he said.

That hopeful message was echoed by the cast, many of whom said the film feels particularly relevant at a time of growing political and social division.

Josh O'Connor, who plays cybersecurity expert Daniel Kellner, said the script immediately resonated with him.

"When the script came through, I read it in one go in a rush and it was thrilling, it felt so needed as it's a film about hope and humanity and understanding."

He suggested that discovering intelligent life beyond Earth could force people to look beyond their differences.

"When there's a lack of understanding of each other, maybe something from outside might unite us.

"I wonder whether the idea of hate is a human invention because none of the documented close encounters are nasty or violent."

The 36-year-old actor also admitted he believes there is likely something beyond Earth, although he is in no hurry for humanity to solve the mystery.