Ewan McGregor stars in Black Hawk Down
Pearl Harbour star Josh Hartnett attended the event along with British cast members Ewan McGregor and Ioan Gruffudd.
The film - which is already tipped for several Oscar nominations - portrays the events of the failed US military mission to Somalia in 1993.
Directed by British-born Ridley Scott, it tells the story of the ill-fated attempt by an elite group of US soldiers to capture hostile warlords in the Somali capital of Mogadishu.
Two Black Hawk helicopters were shot down, and final US casualties totalled 18 dead and 73 wounded.
The US soldiers were part of a UN force trying to arrest local warlord Mohamed Farah Aideed.
After the battle, the body of one of the dead US soldiers was dragged through Mogadishu, in view of television cameras.
The $95m (£66m) film's cast also includes Tom Sizemore.
The actors spent a week training with the US Special Forces in Georgia before filming began and McGregor said it had been an eye-opening experience.
"When you see what those guys go through and experience the camaraderie they share it is very humbling," he said.
Scott, whose other film credits include cult classic Blade Runner and Oscar-winner Gladiator, has denied that the feature is a recruiting film for the US military and described it as an "anti-war" movie.
Speaking at the UK premiere, he said the film was entirely relevant to the current allied action in Afghanistan.
"The film fundamentally discusses two things about intervention," he said.
"First, should we intervene and secondly when should we do that. But it also raises the question about paying attention to what else is going on in the world," he said.
The release date has been moved forward because studio bosses believed it would have resonance with the US and British audiences, he added.
US Defence secretary Donald H. Rumsfeld has already seen the film after joining a special screening for the US military in Washington.