The film’s stars Frances McDormand, Sam Rockwell, Peter Dinklage and Woody Harrelson were among those who witnessed the demonstration.
The UK premiere of an Oscar-tipped film about a mother’s protest against police was itself met with activists as the BFI London Film Festival came to a raucous finale.
Protesters waved banners saying “Picturehouse – it’s time to talk”, “LFF – you let us down” and “still no #livingwage” close to where the stars were arriving on the red carpet for Three Billboards Outside Ebbing, Missouri.
Frances McDormand, Sam Rockwell, Peter Dinklage and Woody Harrelson were among those who witnessed the scenes, alongside the film’s British director Martin McDonagh.
In the movie, McDormand plays a mother furious that months have passed without police tracking down a culprit in her daughter’s murder.
In her anger, she pays for three billboards leading into her town with a message directed at the chief of police, played by Harrelson.
Acknowledging the crowds, cast member Peter Dinklage, known for his role as Tyrion Lannister in Game Of Thrones, joked: “We have protests happening here?!”
He added: “I’m an American, you understand – not being America from the outside – how tricky America is right now.
“It’s not so great, we’re a big pendulum. We swing both ways, we’re never happy – We’ve gotta go one direction, and we’re not happy we gotta go the complete opposite direction.
“I am very sorry for the state of our country right now and the state of our leaders, we need some angry cinema right now.”
McDonagh, who was behind cult hit In Bruges, said: “I kind of like this era of protest, that people are much more vocal and angry than they ever have been before.
“In part the film is quite angry but there’s a lot of humanity and hope in it too, so I think as long as all the anger and protest is mixed with that, I think we’re onto a winner.”
Sam Rockwell, known for roles in The Hitchhiker’s Guide To The Galaxy and Moon, added: “I think it’s an important film, and oddly very timely because of some events that have been happening.”
True Detective actor Harrelson said: “I’ve seen it (the film) in front of a couple of audiences and the response has been pretty electric.
“I don’t know if it’s the protest element – obviously it’s great writing and really well directed and acted and everything, I feel the whole premise of it is pretty heavy but out of that you have incredible humour.
“It’s a wildly entertaining film – I feel it’s gonna do well.”
:: Three Billboards Outside Ebbing, Missouri will be released in UK cinemas on January 12, 2018.