Jack Lowden said it was ''immense'' filming 'Dunkirk'.

The 27-year-old actor plays Spitfire pilot Collins in Christopher Nolan's latest World War Two epic and admitted the filmmaker didn't want to use much CGI, and one day there were more than 1,000 extras on the Dunkirk beach.

Speaking to The I Paper, he said: ''That was immense. He doesn't like to use a lot of CGI, so you would be confronted with this spectacle every day. I think we had 1,200 extras on the beach one day; it was an incredible sight. And the flying scenes were pretty cool. We were up in the air, over the Channel, flying Spitfires, so that was great.''

Nolan - who helmed the hit 'Dark Knight' Batman trilogy - researched 'Dunkirk' by watching real life footage and reading records from the British-led rescue mission in 1940 in which 330,000 Allied troops were rescued from the clutches of the Nazis.

Speaking at the world premiere of the movie London's Odeon on Leicester Square, the 46-year-old filmmaker said: ''I was looking at a lot of firsthand accounts of people who were there. I want people to see it in the big screen and feel like what it was like on the beach or be in small boat. I wanted to make the film feel real. I watched archive footage of what it was like. It was about realism for me and staging it in front of a camera rather than green screen.''

The idea of realism and authenticity was something important for Nolan who even made Harry Styles change the way he tied his shoelaces as soldiers would have done it a specific way.

Styles said: ''When I heard about Chris doing it I was kind of already excited to watch it to be honest and I just wanted to be involved ... On my first day he told me my laces were tied wrong.''

Lowden stars alongside many well-known including Sir Kenneth Branagh and Sir Mark Rylance, others are Nolan regulars such as Cillian Murphy and Tom Hardy, as well as newcomers Fionn Whitehead and One Direction star Styles.