Given that she remains the most iconic woman in the history of cinema, it's remarkable how few A-listers have portrayed Marilyn Monroe on screen. The likes of Ashley Judd and Catherine Hicks have taken the plunge but you get the impression that the bigger stars have always been afraid that any portrayal of La Monroe inevitably ends in caricature.

That's all about to change as we approach the 50th anniversary of Marilyn's untimely death. Angelina Jolie (The Life and Times of Maf the Dog) and Naomi Watts (Blonde) are currently filming stories about Norma Jeane, but it's difficult to see any actress topping the performance of Michelle Williams in this drama.

Based on the best-selling memoir of Colin Clark (brother of Tory diarist, Alan), My Week with Marilyn is the true story of how a young film fan blagged a job with Laurence Olivier's film company just as he was casting Marilyn Monroe in what would become The Prince and the Showgirl (1956). Despite the troubled relationship between Monroe and Olivier, the unwelcome presence of Method guru Paula Strasberg, and the media circus that surrounded the recent marriage of Monroe and Arthur Miller (‘The Egghead and The Hourglass’, etc.), Clark formed a close bond with Marilyn that would seem unbelievable were it not actually true.

Though the story unfolds through the eyes of young film fan Clark (played with a gauche charm by up and coming star, Eddie Redmayne), the heart of the story is Marilyn. This woman was a mass of contradictions: a screen sex siren who was painfully shy; a powerful iconic figure who felt utterly vulnerable in real life; and a woman who was adored but just wanted to feel loved. Williams brilliantly captures all aspects of this personality and shows us not just Marilyn the icon but also Norma Jeane the young woman (36 when she died) unprepared for the spotlight that would follow her every move from the moment she stepped onto a subway grating in a billowing white dress.

It's a superb performance, not least in the sequence when she stands in front of a group of Etonian students and whispers, ‘shall I be her?’ before turning on the Marilyn persona at full power.

With all of the plaudits going Williams' way, it's worth pointing out the quality of Kenneth Branagh's performance. Whether it's that narrow top lip, the despairing glance, or the acerbic Shakespeare line for any occasion, Branagh has completely captured the essence of Olivier. It's another performance that in lesser hands could have resulted in caricature.

As a movie, My Week with Marilyn is a small-scale affair that doesn't always convince on the narrative front, but it contains two towering performances that are likely to be recognised when the Oscar nominations are announced on January 14.

Michael Doherty