WHETHER it’s Brexit, Trump or terrorism, something is leading filmmakers back towards wartime Britain and the stiff upper lip that defied the Nazis. Certainly a number of films are building on that defiant island mentality.

Last year, Their Finest was a charming romantic drama about the writers and thespians making propaganda films for the British Government. Earlier this year, Darkest Hour concerned itself with Winston Churchill’s fight against the appeasers to keep Britain in the war, with Gary Oldman’s Oscar-winning performance maintaining a garrulous lightness amid the drama. Lily James appeared opposite Oldman in that film, as his devoted secretary, and the rising star is front and centre of this latest Second World War feel-good offering, again with a typewriter as her chief prop.

Sharing the amusingly tongue-twisting title from its source novel, The Guernsey Literary and Potato Peel Pie Society is set in two periods: 1941, when the Channel island is occupied by the Germans; and 1946, when London is enjoying a post-war revival but the islanders are still finding their feet.

James plays Juliet Ashton, a young writer who is riding a wave of popularity with a collection of humorous essays. But despite fame, some cash and a dashing American suitor, Juliet is ill-at-ease, mourning the loss of her parents during the Blitz, and unconvinced of her talents.

Distraction, and the sense of something deeper, comes when coincidence leads to a correspondence with a stranger from Guernsey. And when Dawsey Adams (Michiel Huisman) writes of a book club that was formed during the occupation, Juliet abandons her book tour and heads for the island. Flashbacks to 1941 have already introduced the members of the club, which was invented as a cover during a dodgy moment with the Germans. They’re a likeable group, including postmaster Eben (Tom Courtney), widow Amelia (Penelope Wilton), moonshiner Isola (Katherine Parkinson) and Elizabeth (Jessica Brown Findlay), a one-person island resistance fighter. When Juliet arrives on the island in 1946, the group welcome her into their midst, excited at the presence of a celebrity author. But they are without Elizabeth.

Hereon, the story is driven by a number of dynamics: Juliet and Dawsey falling awkwardly in love; Juliet trying to solve the mystery of Elizabeth’s disappearance; the islanders moving on from the traumas and loss of the war; and the writer discovering her true voice. The novel was epistolary. The film, directed by dependable veteran Mike Newell (Four Weddings and a Funeral, An Awfully Big Adventure, Harry Potter and the Goblet of Fire), does involve its fair share of letter writing but its principal device is the flashback, whose purpose is to illustrate what happened to Elizabeth just as Juliet herself is discovering it.

This aspect of the film feels painfully contrived – rather than just one character coming out with the truth in a single sitting, the self-appointed and not always tactful sleuth gets it from them piecemeal. It really doesn’t work. But while the structure can be galling, the film’s blend of pathos, comedy and romance – generated by a clutch of lovely performances – is incredibly winning. Comedy comes for the most part from the bookish islanders’ eccentricity and enthusiasm (Juliet’s first meeting with them is divine); romance from the chemistry between the luminous James and the soulful Huisman; pathos from the back story of wartime hardships, centred on Brown Findlay’s vibrant portrayal of Elizabeth. When Penelope Wilton’s loss-heavy Amelia declares “I’m older than time and I understand nothing”, it’s positively heartbreaking.

James and Brown Findlay are both alumni of Downton Abbey of course, and both growing into splendid actresses. Here, James is the charming fulcrum of events, Brown Findlay the heart.