Directed by Simon Curtis. Starring Michelle Williams, Eddie Redmayne, Kenneth Branagh, Dominic Cooper, Judi Dench, Dougray Scott, Emma Watson, Derek Jacobi, Julia Ormond, Zoë Wanamaker 15A cert, general release, 99 min

IN THE SUMMER of 1956, a young toff called Colin Clark (brother of Alan, son of Sir Kenneth) landed a job as third assistant director on The Prince and the Showgirl, a star vehicle for Laurence Olivier and Marilyn Monroe. Clark's account of the fraught production was later published as The Prince, the Showgirl and Me.

Eyebrows were raised when a follow-up, called My Week with Marilyn, arrived in 2001. The first book depicts the working life of a gofer; the second suggests that Clark and Monroe were intimately involved. Huh?

This unlikely story forms the basis of Simon Curtis’s unlikely movie, a slight little doodle bolstered by an all-star cast. Here, Clark (the hugely likeable Redmayne) becomes one of Monroe’s emotional props when exhausted husband Arthur Miller (Dougray Scott) returns to the US.

Marilyn already boasts an army of such psychological assistants. Her business partner Milton Greene (Dominic Cooper) is on hand with pills for sleeping, pills for waking and pills for just in case. Paula Strasberg (Zoë Wanamaker), Monroe’s method acting coach, hovers over her every move and attempts to get through the performer’s addled fug.

Between takes the star bonds with Clark, who escorts her around England, much to the chagrin of the girl in wardrobe (Emma Watson in a blink-and-you’ll-miss- her role) he’s supposed to be dating. The romance, like the movie, comes to nothing. Sure, Kenneth Branagh has a ball with Olivier’s clipped vowels and self-regard, and Judi Dench is just adorable as Dame Sybil Thorndike. However, the perennially miserable Michelle Williams, despite a decent performance and gallons of peroxide, looks distractingly unlike Monroe.

It's nobody's fault: Marilyn Monroe's stilettos are simply too big for any actor to fill. For all the thespian quality on offer, My Week with Marilynfrequently plays like one of those terrible late-night TV biopics: "Dodi, do you think we can escape the paparazzi if we go through that Parisian tunnel?" or "Ringo, do you want to come with meand Paul and George to visit the Maharishi Mahesh Yogi in India?"

Williams does good work, but as Monroe herself might have observed, there’s only so much a girl can do.