It appears that Winston Churchill has become the new King Lear—the role that British actors of a certain age are simply expected to play as a sort of career capstone, a necessary rite of passage. (Americans are not excluded, either, as witness John Lithgow’s recent turn in “The Crown.”) “Darkest Hour” provides Gary Oldman with his chance to play the Prime Minister, and though even with plenty of makeup he’s hardly the spitting image of Churchill—at times he looks more like Miles Malleson—he does capture the man’s bulldog pugnacity. It’s no wonder that Oscar buzz has already started around him.

Churchill’s tenacity is tested, however, in the events of the period that writer Anthony McCarten and Joe Wright have chosen to concentrate on—the weeks of May and June, 1940, when Hitler’s assault on France had left the British forces sent to the continent stranded on the beach at Dunkirk and Neville Chamberlain (Ronald Pickup, who took over the role originally slated for the late John Hurt) was forced to resign as PM. Though he would have preferred that his Foreign Minister Lord Halifax (Stephan Dillane) succeed him, the taint of the policy of appeasement that the government had followed, along with other considerations, led to the recommendation of Churchill to King George VI (Ben Mendelsohn), and the monarch, despite his dislike, offered him the post.

Much of the narrative has to do with pressure on Churchill from Halifax, and to a lesser extent Chamberlain—both members of the War Cabinet he cobbled together—to enter into negotiations with Hitler, through Mussolini, to cease hostilities and thereby rescue England’s trapped army. In this retelling, the two actually conspire to bring Churchill’s ministry down by threatening to resign from the cabinet if he refuses to consider their proposal. (In reality, it seems that the script ratchets up the degree of Machiavellian manipulation, especially on Halifax’s part, for dramatic effect.) And Churchill is assailed by self-doubt: he remembers—and is sometimes reminded by others of—how his Gallipoli endeavor had ended in disaster in 1915.

Yet Churchill soldiers on, coming up with the idea for Operation Dynamo—the use of a fleet of small, mostly private boats to cross the Channel to Dunkirk and save the stranded army—while gauging public opinion on whether the nation should continue fighting despite the long odds and the failure of the United States to offer any appreciable assistance. In one scene, a desperate Churchill is infuriated when a telephone call to President Roosevelt, portrayed here as a supreme trimmer, accomplishes nothing but an increase of frustration.

The historicity of that call is debatable—U.S. law tied Roosevelt’s hands, after all, and ultimately he found a way to work around the restrictions on supplying arms to combatant nations—but another of McCarten’s scenes, in which Churchill escapes his chauffeur to take a ride on the underground and talk with “ordinary folk” about what he should do—is utter invention, and, it must be said, grossly saccharine invention. Still, It fulfills the function of dramatizing how the PM was bolstered in his determination to fight on by the indomitable grit and fortitude of the British citizenry. After that fictitious time on the tube, Churchill goes to Parliament to deliver his stirring speech—a masterpiece of rhetoric—about never surrendering.

Though one can quibble about that subway visit and the portrayal of Halifax (as well as the quick warming of George to his new PM), however, “Darkest Hour” gets the essence of Churchill’s predicament between Chamberlain’s resignation and the beginning of the Battle of Britain pretty much right; certainly it doesn’t indulge in the almost surreal flights of fantasy about Churchill’s second thoughts about D-Day that marred the recent “Churchill” (in which Brian Cox cut a fine figure as the PM). And Oldman, despite having to overcome some physical (and vocal) limitations, makes Churchill the towering presence he undoubtedly was.

The supporting cast is fine—not just Pickup and Dillane, but Mendelsohn too, along with Kristen Scott Thomas as an ever-supportive Lady Churchill and Lily James as his new secretary Elizabeth, who has to come to terms with her boss’ eccentricities while dealing with her own personal concerns about men in combat. Wright keeps the picture’s canvas relatively small, but along with eliciting strong performances he has gotten stellar contributions from the technical crew—production designer Sarah Greenwood, cinematographer Bruno Delbonnel and editor Valerio Bonelli—although the music score by Dario Marianelli italicizes the action too readily.

One wonders about the current avalanche of Churchilliana on screen—even Christopher Nolan’s “Dunkirk,” in which the PM doesn’t actually appear, can’t avoid using his words as a peroration. Perhaps the answer lies in the fact that filmmakers believe it valuable to be reminded that a leader of principle, steadfastness and vision is an actual possibility at a time when such qualities are in abnormally short supply among politicians. From an historical point of view, there are aspects of Wright’s film one might debate, but, capped by Oldman’s strong performance, it’s one of the better recent films about the great British statesman.