Miss Pettigrew Lives for a Day (PG) Star rating: **** Dir: Bharat Nalluri With: Frances McDormand, Amy Adams, Shirley Henderson, Ciaran Hinds

If her Oscar-winning performance as a no-nonsense police chief in Fargo wasn't enough to make you realise that Frances McDormand isn't at least as talented as her contemporaries Meryl Streep and Susan Sarandon, her lead role in this enormously entertaining British period romp ought to do the trick. While McDormand probably won't get another Oscar nod for her turn as a destitute ex-governess who is unexpectedly flung into London high society, it should at least shove this criminally underexposed actress some way towards the limelight she merits.

Based on the one-time bestselling, long-forgotten but recently rediscovered 1938 novel by Newcastle-born writer Winifred Watson, Miss Pettigrew Lives for a Day, which had its UK premiere at the Edinburgh International Film Festival in June, is set in London on the eve of the Second World War. Guinevere Pettigrew finds herself out of work and seemingly terminally unemployed thanks to her firm character, moral backbone and inability to keep her trap shut when faced with a fool.

Desperate times call for desperate measures, and following a dispiriting night spent queuing in the cold at a soup kitchen she determines to masquerade as hired help from her old employment agency. Luckily, the first potential employer Miss Pettigrew presents herself to turns out to be a dizzy nightclub singer named Delysia LaFosse (chocolate-box sweet Amy Adams, whose performance is clearly inspired by Marilyn Monroe). She is only too eager to employ Miss Pettigrew after she makes quick work of sorting out a terrible early-morning mess she's got herself into with three men: an amorous theatre promoter's son (Tom Payne), a sleazy club owner (Mark Strong) and a penniless pianist (Lee Pace), who's quite clearly the love of the girl's life.

In return for services tendered, Delysia promises the bedraggled and mousey-looking Miss Pettigrew a makeover that will transform her into a striking, stylishly attired woman, and after that's done the odd couple step out on a whirlwind 24-hour tour of the capital that encompasses a fashion show, a cocktail party and a nightclub act. As the day progresses, with Miss Pettigrew continuing to advise the hopelessly confused Delysia about matters of the heart in her new role as personal secretary, she is introduced to Delysia's dubious celebrity fashion stylist friend Edythe Dubarry (Shirley Henderson on wickedly snappy form). Having spotted Miss Pettigrew at the soup kitchen the previous night, the calculating minx attempts to blackmail her into smoothing over a row she's had with her beau, the robust millionaire ladies' underwear designer Joe Blumfield (suave Ciaran Hinds) to whom Dubbary's engaged and behind whose back she has been caught cheating.

Smartly scripted by US-British team David Magee (Finding Neverland) and Simon Beaufoy (The Full Monty), and snappily directed by Bharat Nalluri, who's been working in British television directing episodes of Spooks and Life on Mars, Miss Pettigrew Lives for a Day positively whizzes along from one wittily comic and stylishly dressed set-piece to the next. McDormand dazzles with a wonderfully naked, natural and nuanced performance that would charm the spats off a spiv. But although the glitzy and glamorous proceedings play like a cross between a Noel Coward farce and a Fred Astaire musical, there's also a quite bit of substance beneath the champagne fizz.

Miss Pettigrew's initial misfortune shows the miserable alternative to the high life that was the daily grind for most Londoners - and people elsewhere in Britain, no doubt - during the period between the wars. And with Delysia torn between effectively prostituting herself to ensure her financial security and chancing poverty with her insolvent true love, the high life itself is swiftly revealed to be morally bankrupt. That gulf of experience between the elderly poor and the wealthy young is cleverly summed up in a telling scene towards the end of the film, when British bomber planes are flying over the streets of London while the rich continue to revel on the rooftops. Commenting as a pair of Britons who have already lived through one world war in which they both lost loved ones, Miss Pettigrew and Blumfield note with concern the revellers' utter obliviousness to the dreadfulness of the looming conflict.

It's not too much of a leap to see how all that resonates with the state of the nation today, what with the economic downturn, the widening gap between the privileged and the non-privileged and the continuing conflict in the Middle East. The social, political and moral commentary in the film, however, remains beneath the surface, there for those that care to look for it. For those viewers who just want the champagne fizz, meanwhile, this fast-paced, super-stylish and charismatically acted period drama boasts many magnums' worth of it.