The trouble with being Ralph Fiennes is that, on a good day, firing on all thespish cylinders, you tend to make everyone around you look completely rubbish. He did it before in the political allegory Land of the Blind, and there was even a touch of it in The Constant Gardener.

In The Duchess, however, a period movie filled with neophyte actors and wannabe starlets, Fiennes is on punishingly good form, a dazzling cynosure surrounded by stiff gestures and self-conscious poses. He is William Cavendish, the fifth Duke of Devonshire, a fabulously dyspeptic and slightly fey 18th-century aristo who loathes inter-personal communication, displays affection only for his English pointers and greets the news that his firstborn is a healthy baby girl with the peevish retort, “I asked for a male heir!”

William is married to the fashion-obsessed celebutante Georgina Cavendish (Keira Knightley), who was born, so the marketing blitzkrieg reminds us, Georgina Spencer, and was thus a distant aunt of the late Diana, Princess of Wales. “This summer, history repeats itself!” screams the movie’s craven, and erroneous, tagline. Though, true, for the first 15 minutes it’s fun to play the duelling Dianas game and to match Knightley’s Spencer with her great-great-great-great-grand-niece, ie Oooh look! She likes fashion! And look! She’s kind of a celebrity too! And, er, she’s a crusader! (The duchess, apparently, was an avid politico and liked Whigs with her wigs).

The Diana-spotting novelty quickly wears off (around the overblown line: “I give you the Empress of Fashion herself!”), and all you’re left with is a movie about a really rich girl married to an even richer guy who can’t express his feelings but has lots of houses and even more servants. And there, of course, is the rub. For beneath the hype and tabloid traction, the movie is dramatically flaccid. Georgina marries William, he’s rude to her, he has an affair, she has an affair, and then they kind of get on with it.

Perhaps if Fiennes was a lesser actor he might have made William more of a monster. Instead, he has found in William a vaguely sympathetic yet cruelly limited man who can only meekly declaim to his crestfallen wife: “I love you, in the way I understand love.” Facing Fiennes, the junior cast, like lambs to the slaughter, go to pieces. Knightley gives great profile (just as she gave great close-up in Edge of Love); Dominic Cooper plays her lover, Charles Grey, as a one-note automaton; while Haley Atwell’s strumpet Bess is wonderful at saucy stares but struggles with the spoken word. In short, Fiennes: 4, Kids: Nil.

12A, 110 minutes

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