Readymade to play on an endless loop on Freeform’s 25 Days of Christmas for the next decade — or at least as long as actual TV channels continue to exist — “Last Christmas” is as flimsy and disposable as holiday wrapping paper with just as much substance. But this isn’t just future fodder for Freeform; it feels more like the big-budget, well-acted version of an original Hallmark Channel Christmas movie whose writers based their entire film on a song title, rather than beginning with a real plot idea. That would be bad enough coming from a scribe you’ve never heard of who wrote three episodes of “Melissa & Joey”; instead, “Last Christmas” arrives from Oscar-winning screenwriter Emma Thompson. You’ll blush your way through this bad, but basically pleasant, holiday rom-com, and it isn’t because of the love story: it’s because you feel embarrassed for everyone involved, who are doing far better work than the only fitfully funny script deserves.

That everyone includes screenwriter and co-star Thompson, “Game of Thrones” queen Emilia Clarke, and “Crazy Rich Asians” stars Henry Golding and Michelle Yeoh. Rob Delaney and Peter Serafinowicz are listed in the credits, but don’t get too excited like I did: they’re here for all of a minute. Behind the scenes, Paul Feig is at the helm, turning in his least funny movie since “Unaccompanied Minors.” Everyone here is slumming it, and it’s unclear exactly who’s doing whom a favor, though they all must owe someone big.

Set in December 2017, “Last Christmas” stars Clarke as Kate, a selfish young woman in London who works as an elf at a year-round holiday store, packed with tacky decorations and holiday cheer. She halfheartedly works for a boss she calls Santa (Yeoh), who in turn calls her “Lazy” and misses the days when Kate was a dedicated worker. Kate’s Croatian refugee mother (Thompson) worries about her daughter’s health after she had a mysterious operation and hasn’t been the same since. But when Kate meets a guy named Tom (Golding), her perspective on her life begins to change, as she spends more and more time with him. But he keeps disappearing …

Co-written by Thompson and Bryony Kimmings and based on a story by Thompson and her husband, Greg Wise, “Last Christmas” cobbles together a bunch of half-baked ideas, all set to the songs of George Michael. Other than the title track — which flat-out spoils the movie’s big reveal — songs feel shoehorned in, particularly “Freedom,” which is too big of a hit to skip but doesn’t feel right for the moment it plays over. The comedy bits often fall flat, despite the best efforts of the people on screen, though the off-kilter editing from Brent White is as much to blame as the script. Commentary on the refugee crisis and Brexit feels tacked on, and character development is either made far too obvious in dialogue or left entirely to the actors to do, depending on the scene.

The cast is what makes “Last Christmas” the type of movie you’d half-watch while sleepy drunk on mulled wine, rather than actually go to the trouble of turning off. Thompson gives herself the best lines as the overbearing Balkan mother, and this is more proof after “Crazy Rich Asians” that Yeoh should continue to do comedy. As the leads, Clarke and Golding twinkle like classy white lights amidst gaudy strewn tinsel. He charms, overcoming a role that’s written as a blandly perfect guy, making both Kate and the audience swoon. Clarke is vivacious and beguiling, making her character likable even in her selfishness.

As is abundantly clear from the beginning of the film, “Last Christmas” has a big twist in the third act, though you’ll likely have it all figured out by the time of the “reveal.” But even knowing the twist ahead of time, it tugs at the heartstrings and mostly still works.

“Last Christmas” is like a tree decorated by a child: ornaments are haphazardly hung everywhere, and it’s all a bit of a mess. But there’s a seasonal charm here that is difficult to deny, even while you’re staring in wonder at the baffling choices made by Feig and Thompson at practically every turn. However, for all its flaws, “Last Christmas” isn’t a bad time, despite being a bad movie. Credit Clarke and Golding — or that rum-heavy egg nog you should drink before the opening credits. [C-]