Four Christmases in one day sounds an awful prospect. But far worse is the realisation — upon meeting Californian couple Brad and Kate — that these two unmarrieds are going to learn things about themselves as a result of the 24 festive hours they must spend with each of their divorced parents in turn.

Vince Vaughn and Reese Witherspoon play the leads. Do they convince as lawyers or lovers? No. Do they convince as space aliens trying to infiltrate the human race? Yes. Unfortunately, no one, not even the film’s director, Seth Gordon, ever twigs.

The script, an awkward mix of generic gags and indulgent improv, has a few bright spots. Robert Duvall plays Brad’s desiccated, macho dad, Howard. At one point his son unexpectedly returns to the homestead. Says Howard, with a cackle: “Did you forget your tampons?”

Meanwhile, Brad’s mum, Paula (Sissy Spacek), a gentle therapist, reveals a darker side while playing the party game Taboo, wielding the penalty buzzer like a Taser gun.

This is a vehicle meant to show off the talents of Vaughn and Witherspoon but it exposes them as relics from the past. He was an angry young man, she seemed a natural heir to Katharine Hepburn — where did all that spark go?

Spacek and Duvall, by contrast, look as good as ever — you believe they were once a couple, that she moved on and he didn’t. A comedy with them in the lead — now that’s what I’d like to find in my stocking this Christmas.