First Washington, now London. Gerard Butler’s Secret Service agent Mike Banning exhibits his gung-ho, he-man talents and exceptional marksmanship to save President Benjamin Asher (Aaron Eckhart) a second time in this sequel to the surprise 2014 hit that actually overshadowed its bigger, flashier competitor “White House Down.” Crammed with collapsing British landmarks and masked bad-guys being gunned down in droves (as well as tons of implausibility), this follow-up to “Olympus Has Fallen” is every bit as dumb as its predecessor. But that probably won’t bother the armchair patriots who thrive on such bombastic, jingoistic claptrap.

The flimsy plot begins when the sudden death of the British prime minister leads to a state funeral in London to which scads of world leaders, including Asher, will come. (The sole exception, we’re told, is the Russian president—a typically offhanded, humorless jibe in the script cobbled together by no fewer than four screenwriters.) Unbeknownst to all, the sad ceremony has been arranged by the evil Aamir Barkawi (Alon Moni Aboutboul), a wealthy Pakistani arms dealer, as an occasion to take revenge on the West for the death of his daughter in a drone strike on her wedding reception. The entire British force of security personnel—police, soldiers, even palace guards—has been infiltrated by what appear to be hundreds of swarthy terrorists who mow down civilian observers, cops and heads of state alike on the steps of St. Paul’s and at Buckingham Palace while blowing up London Bridge, the Houses of Parliament and any number of other photogenic sites. (The level of incompetence assumed in Blighty’s government here is astronomical.) Barkawi himself watches the mayhem from a hidden location in Pakistan, but his son Kamran (Waleed Zuaiter) is directing the operation on site, hoping to capture Asher and behead him in a broadcast that will reach a global audience.

Unfortunately for Barkawi’s plans, though his minions take out presidents and prime ministers in droves, Asher and Banning (along with Banning’s boss Lynne Jacobs, played by Angela Bassett) escape after a prolonged car chase and ill-fated helicopter ride. Asher and Banning are left on the run in the London streets, eventually taking refuge in an MI6 safe house with a savvy British agent (Charlotte Riley). But they’re quickly on foot again as Barkawi’s men arrive at the place, leading to the long-obvious conclusion that there must be a mole within British Intelligence. Rest assured, however, that this plot thread will not lead to anything remotely resembling a John Le Carre novel. In fact, in the end it will be disposed of as an insignificant afterthought.

Instead the scripters and journeyman director Babak Najafi focus their attention on the really important stuff—the heroics of Banning, especially in mounting a climactic assault on the Barkawi compound after Asher has been taken and his execution is imminent, and the steely, determined efforts back in the White House situation room to help the jut-jawed hero. These are led by unflappable Vice President Allan Trumbull (Morgan Freeman), who smoothly issues order to his team, among them General Edward Clegg (Robert Forster), head of the Joint Chiefs; Secretary of Defense Ruth McMillan (Melissa Leo); White House Chief of Staff Mason (Jackie Earle Haley); and Ray Monroe (Sean O’Bryan), Deputy Director of the NSA. These stock figures make little more than cameo appearances, and the actors playing them are thoroughly wasted. But the mere presence of Freeman assures us that all will be well and the dastardly villains properly dealt with; in the end, indeed, it’s left to Trumball, for some reason, to deal with the elder Barkawi, and to deliver a reassuring address to the nation. Curiously, Asher has disappeared into the woodwork.

But not, of course, until Banning has saved his hide again. Butler once more glowers and scowls through the role, pausing intermittently to bark out orders or deliver what passes for a humorous remark in this sort of juvenile nonsense. There’s an attempt to humanize Banning by providing him with a pregnant wife (Radha Mitchell, also reduced to a cameo) and having him fret over whether to resign his White House post to protect his family-to-be, but the actor’s impassivity is an insuperable obstacle. Eckhart can’t really make us believe in Asher as a regular-guy chief executive who can man up when danger threatens and blow up the bad guys too, but he’s at least inoffensive. As for all the doomed extras, they die for the most part quickly without much blood being shed; the effect is like a shooting gallery with clay pigeons as the targets. The R rating is explained not so much by the violence as by the regular dropping of one obscenity in particular by the irascible Banning, whose xenophobic remarks to the bad-guys he’s about to eliminate are apparently intended to arouse nationalistic fervor but instead come across as depressingly ugly.

The picture’s physical production is okay, with Ed Wild contributing decent cinematography and editors Paul Martin Smith and Michael J. Duthie working overtime trying to give energy and edge to action scenes that frankly run on too long, bloated not only by the repetitive visuals but by Trevor Morris’ overblown score. But certainly what most viewers will remember is the work of the special effects team—adequate rather than awesome—who appear to have had great fun staging the explosions that take down one famous London site after another. You have to wonder whether there will be any world landmarks left to demolish for the delectation of the masses by the time the upcoming sequel to “Independence Day”—which started the unhappy trend of trashing iconic buildings as a cinematic staple—is released later this year.