Starring Gerard Butler. Rated 14A.

How many screenwriters does it take to space out a seemingly endless string of explosions? Well, according to London Has Fallen, no fewer than four. They have the eager assistance of director Babak Najafi, who layers on the violence with such relish that we become slaves to a kind of gun-barrel porn, where mindless sex is replaced by the constant spray of bullets.

This is the completely superfluous sequel to 2013’s Olympus Has Fallen, in which Secret Service agent Mike Banning (Gerard Butler) saved American president Benjamin Asher (Aaron Eckhart) from a relentless wave of swarthy terrorists. This time around, Banning and President Asher are in London to attend the funeral of Britain’s prime minister. Within minutes of the opening, the obligatory onslaught of swarthy terrorists—disguised this time as London cops—blows up five attending heads of state while destroying virtually all of the city’s major landmarks.

Local moviegoers may be upset that Canada’s fictional prime minister, who looks as if the casting people took their cue from watching old clips of Brian Mulroney, is one of the first to go. Luckily, Asher manages to survive through a virtual orgy of violence.

From there, Banning and the president must make their way along the ruined streets in search of sanctuary. Despite the long-distance technical support of the vice-president (Morgan Freeman), things get rough for democracy.

After a while, you begin to welcome yet another explosion, if only because it drowns out the sporadic bursts of jingoistic dialogue. While beating the crap out of a terrorist, Banning tells him: “Here’s what you guys don’t understand. We’re going to be around for the next thousand years!” Fine by me, as long as they quit making movies like this.