The charming, affecting Their Finest pays homage to the films of World War II

Historical epics have taken it on the chin lately, between the pretty but superficial Queen of the Desert and the earnest but inert The Promise. Solemn and self-important to a fault, both could have used the relaxed, jaunty brio that fills Their Finest, a World War II comedy that, despite its light hand, never compromises the grief and loss that lie at its core.

Adapted from Lissa Evans' 2009 novel Their Finest Hour and a Half, the movie follows a group of screenwriters tasked with creating propaganda for the British war effort, in the midst of the London blitz. Recruited after the Ministry of Information spies some of her clever lines in the newspaper, newcomer Catrin Cole (Gemma Arterton) is assigned to write "slop" - otherwise known as women's dialogue - in films designed to boost national morale.

Leaving her husband, Ellis (Jack Huston), an artist and wounded Spanish Civil War veteran, at home, Catrin plunges into the world of women's work, propaganda and showbiz, befriending a cynical colleague named Buckley (Sam Claflin).

Sneaking in some proto-feminist female agency into her storylines, she becomes the trusted script doctor to Ambrose Hilliard, a semifamous actor who is cast in Catrin and Buckley's latest production, about the evacuation at Dunkirk.

That vain, rather silly fellow is played by Bill Nighy, in a performance crafted to pilfer every scene he's in. Lanky and spaghetti-limbed, Nighy provides much of the comic relief in Their Finest, which lovingly lampoons the cockamamie cavalcade of cinema, especially the sausage-making ritual whereby a real-life story becomes massaged into stirring, audience-friendly entertainment.

It's no surprise when Catrin becomes ensnared in a romantic triangle with the two men in her life. What's genuinely startling is how director Lone Scherfig spikes the romance and comedy with stark moments of violence, as characters we come to know and love succumb to German bombs and, sometimes, less predictable calamities.

Working from a script by Gaby Chiappe, Scherfig - best known for the winsome coming-of-age drama An Education - skilfully keeps the tonal shifts in working order, keeping the story afloat in a series of crisp, sharply focused vignettes awash in clattering typewriters, smouldering cigarettes and other appurtenances of a bygone age.

Bill Nighy stars in Their Finest.

The plot thickens when a government official insists they rewrite the Dunkirk movie with an eye towards drawing America into the war. At this point, Scherfig creates a wonderfully corny movie-within-a-movie, replete with melodramatic deaths, daring rescues, a cute dog and a rather random American character played with period-perfect wholesomeness by Jake Lacy.

In an unexpected twist, much of what's played for hyperbole in the fictional film presages what happens in Their Finest, during which Catrin comes into her own, like so many women of her generation. Buoyed by Rachel Portman's lilting score and a pleasing visual and production design, Their Finest is an old-fashioned movie about old-fashioned movies, where sincerity and optimism can often look like kitsch, but in which values are rightfully celebrated, without a trace of condescension.

They may not make movies like they used to, but Their Finest is a sprightly, charming example of why it's at least worth making movies about the way they used to make them.