Time for another outbreak of world war twee: a glutinous 40s-period exercise in British rom-dram solemnity, as if Downton Abbey were subject to a very polite Nazi occupation. (There are three graduates of that TV series in this film, and it might have been sufferable over four or five episodes at Sunday teatime.) Just reading the cutesy title made me lose the will to live halfway through.

Lily James plays Juliet Ashton, the bestselling British author of witty but shallow wartime vignettes, who is engaged to a terribly handsome American. But now the war is over, she is yearningly dissatisfied and longs for something to tap creatively into the real pain that is still in her heart (the film gestures at the bereavement she suffered in the blitz). I should admit that James does her best with all this, and wears 40s fashions with some style.

Then Juliet gets what amounts to a fan letter from one of the handsomest pig-farmers in the world, a stubbled exquisite called Dawsey Adams (Michiel Huisman), based in Guernsey. Juliet heads down there to speak at the eccentrically named local Guernsey Literary and Potato Peel Pie Society, and meet the gallery of adorable lite-eccentrics (played by the likes of Tom Courtenay and Penelope Wilton) whose society was born in semi-defiance of the German occupation.

Soon Juliet uncovers a painful secret, whose details are revealed and then quickly passed over. We meet a good German, a chap who helps in Dawsey’s farm like a sort of Wehrmacht James Herriot. We hear about a child who works at the island’s slave labour camp, and about a horrible moment at a concentration camp. That child, and the camp, occupy the briefest flashbacks and largely off-camera moments, before we’re whooshed back to picturesque cosiness and comfiness. Christopher Menaul’s recent movie Another Mother’s Son tackled the Channel Islands occupation with more candour. Escapist fun is great, but this is icky and naive.