My Week With Marilyn (15), ***

Marilyn Monroe had a lambent quality on screen. Her face seemed to glow out at the audience. As much as her physique, it was the way she photographed in close-up that gave her that mysterious appeal. Against huge odds, the brilliant American actress Michelle Williams manages to capture the Monroe mystique. Her uncanny performance lends an extra charge to what might have otherwise seemed a very middling 1950s period piece (albeit one full of excellent character turns).

My Week With Marilyn tells the tale of Colin Clark (Eddie Redmayne), a drippy Englishman in his early 20s, ex-public school and Oxbridge, who has a hankering to work in the film industry. It's not an ambition that his father, Kenneth (of Civilisation fame), takes seriously. Clark's persistence eventually wins him a job as a third assistant director on The Prince And The Showgirl, the film that Sir Laurence Olivier is about to make at Pinewood Studios with Monroe. Olivier is played wonderfully by Kenneth Branagh. He mimics Olivier's clipped diction, plays up his campness and vanity, while showing his strange mix of vulnerability and drive. The Olivier here may be self-absorbed and prickly, but he knows Monroe has qualities he doesn't have.

The director, Simon Curtis, does a fair job of capturing the "Rankery", as Pinewood Studios used to be nicknamed in the 1950s, when the Rank Organisation was busy making its Doctor In The House and Norman Wisdom comedies. The studio is full of technicians in jackets and ties. We catch a passing glimpse of Wisdom in his cloth cap. There is a tremendous scene early on when the cast assembles for a first read-through. Monroe, inevitably, is late and flustered. Dame Sybil Thorndike (Judi Dench at her most emollient) tries to comfort her, but it is clear Monroe feels as if she is on Mars as she sits down with all these eccentric and mannered British actors. For their part, they're utterly bewildered by her adherence to "the method", and cannot begin to understand why she needs an acting coach (Zoë Wanamaker's Paula Strasberg) on set with her at all times.

In its lesser moments, this film resembles a self-conscious British TV drama; it caricatures Englishness at every opportunity. As we flit from the thatched pub where Clark stays during shooting to the library at Windsor Castle or from Eton College to London Airport, it's as if we're caught in a theme-park version of England. Not even Working Title at its most shameless in the Notting Hill-era offered quite such a roseate, tourist-eye view of England.

The most problematic character in the film is Clark himself. Curtis and screenwriter Adrian Hodges resist the temptation to portray him as an Ian Carmichael silly ass-type. As played by Redmayne, he is posh but pragmatic. He is continually getting the production out of a fix. What is very hard to understand is why Monroe, then the biggest movie star in the world, would be so drawn to such a chinless wonder.

It's left to Williams, surely a front-runner when the race for best actress awards starts in earnest in a few weeks, to lend emotional urgency to the film. Thankfully, she doesn't play Monroe as victim. Nor does she try to send up cinema's most voluptuous icon. Instead, her Marilyn is febrile, highly-strung and playful. By turns, she is open to the outside world and suspicious of it in the extreme.

Occasionally, the film hints at the snobbery and class tensions that riddled the Britain of the era. Clark, we are always aware, is from a background of privilege. Working in films is, for him, slumming it. He is a bland protagonist, but with Williams' blazing performance as Marilyn, that scarcely seems to matter.

Anthony Quinn is away