The temptation to spin it into a franchise was too great to resist. Now the action shifts to London for more Taken-style violence. "Everybody got to break out in this movie really," says Butler of the shift in location. "We got to have more international story and to make it more on the road, so we're travelling all over. What was great about the first movie is that it was claustrophobic. But this has got a bigger, crazier, more intense canvas."

Gerard Butler stars in the second film of the series

When he made the original, a sequel was the last thing on his mind. "When I first took this on," Butler says, "it actually seemed just like a fun movie that would be provocative and maybe have a bit of a message in there. I didn't for a second think 'franchise'. Then the movie did really well, and I love seeing the reaction that audiences have to it. And then you think, yeah, maybe you've created something here that you could run with."

Butler enjoyed consulting with real Secret Service agents and security professionals so he could give the movie a veneer of believability while appealing to more grown-up audiences. "We thought, 'Let's push it to the limits, let's really try to examine what would happen there,'" he says. "In playing the character and also thinking out the story, you ask what is the protocol, what are some of the things you would do, and then how can we dramatise that, how can that lead to a situation? And we wanted to make it as brutal and uncompromising as it would be. Although I didn't realise when I made the first movie how many people I stabbed in the head. Now that's my signature move! What can I say?"

Born in Scotland, Butler also had some strong opinions on the film's UK setting. "There was a big fight I had on the movie because at one point they were going to take out Big Ben," he says. "But I said no. I didn't want to take out London Bridge or Big Ben. So we ended up taking out Chelsea Bridge instead. And Westminster Abbey. Because you do want something that's gonna really spark like watching the White House fall down."

Watch the trailer for London Has Fallen here: