You know that elephant in the room, the one everyone tries to ignore? Well, this film has one of those. But the elephant in An Education doesn’t just stand there in the very structure of the film. No, it breaks wind, it defecates, it howls and then takes a bow — and still the film carries on as if there’s no elephant. Yes, I know what you’re thinking: what is he on about?

Let me explain. An Education is based on a memoir by the journalist Lynn Barber and written by Nick Hornby. It’s 1961. Officially, the 1960s have begun, but for bright and bored 16-year-old Jenny (Carey Mulligan), growing up in the dull suburbs of Twickenham with her pushy parents (Alfred Molina, Cara Seymour), it might as well be 1951. Jenny is planning to go to Oxford, but is eager to grow up fast and get an education in sophistication. She dreams of a life less ordinary: reading Camus, wearing black, smoking, listening to Jacques Brel and talking about books and existentialism. Her ticket to that brighter world turns up in the form of David (Peter Sarsgaard), a charming, handsome older man in a cool car. He’s rich, and he starts to date her.

Impressed by his charm and celebrity connections, Jenny’s parents are quickly seduced by David and give their consent to his courtship. We, the audience, are meant to be seduced, too. The film wants us to believe there’s nothing dubious about an older man wanting to introduce a young girl such as Jenny to the finer things of life, such as classical music, Paris, painting and his penis. Ooops. Don’t mention the P-word. Because nobody does. David’s sexual longing for Jenny is the elephant in the room, the thing everyone ignores — Jenny, her parents, her friends, even the film. It’s only later, when David is shown in a different light, that we are invited to become disapproving. But you can only go along with the film’s reticence if you ignore what your instincts tell you: here is a much older man who wants to have sex with a young girl and uses the trappings of his sophisticated life and friends — the glamorous Helen (Rosamund Pike) and Danny (Dominic Cooper) — to this end.

The film’s accepting attitude to their liaison is well illustrated during a weekend away together. In their bedroom, Jenny tells David she wants to wait until she is 17 before she loses her virginity, and he is very understanding. Then he asks to see her breasts. She gives him a peep, and he politely replies, “Thank you”. The scene is played like a happy trade-off between two innocents. Hello? This is creepy.

That would be fine if we were in Patricia Highsmith or Patrick Hamilton territory, but the Danish director Lone Scherfig keeps the first half all bright and breezy. So instead of being a dark and dirty story about male desire and deception, An Education is a bittersweet but ultimately upbeat coming-of-age tale. Things come to a head when David offers to marry Jenny, and she must choose between Oxford or becoming his wife. What does Jenny think of David? In Barber’s memoir, it’s clear she doesn’t really like him, but we never get inside her head, or his, to find out.

I wish An Education had been less timid and more edgy, especially when it comes to the complicity of Jenny’s parents. Barber has written that they “had practically thrown me in bed with him”, but here they are mere innocent dupes. So when the big revelation arrives in the final act, it doesn’t leave you as startled or as angry as you should be. One gets the feeling that for all concerned, it’s nothing more than a ghastly mistake.

That said, An Education offers plenty to enjoy and admire. It’s full of first-rate performances. The American Sarsgaard is totally convincing as a charming Englishman. And the much-underrated Olivia Williams brings real depth and heart to her role as Jenny’s teacher, Miss Stubbs. The raves for Mulligan’s performance are deserved — though there’s no way a 16-year-old girl would talk with the tone of confidence Jenny has. Just shut your eyes and listen to her speak and you’ll hear what I mean. And Hornby hasn’t lost his touch when it comes to the secrets of the male heart. There’s a very moving scene when Jenny’s dad brings her a cup of tea and, standing outside her locked bedroom door, talks about his own fear of life. Hornby also captures brilliantly a type of young English girl, both precocious and pretentious, who I doubt exists any more: one in love with books and culture and all things French. Does the Simon Cowell generation even know who Albert Camus is?

If An Education doesn’t look or sound like a film about the 1960s, it is one of the better ones about that decade. For while it can see the boring life of the suburban 1950s, it knows the glittering goodies that would come with the 1960s weren’t always so golden.

12A, 100 mins

Editor's choice

• The 100 Best Films of 2009
• The 100 Worst Movies of 2009
• The 100 Best Films of the Decade