La Fille mal gardée, Royal Opera House, London

Despite its title, this ballet is an utterly English romcom, complete with clogs and dancing chickens

London audiences in 1791 called it "Filly me Gardy". Now fans refer to it with a single syllable: "Fille". The old French title of La Fille mal gardée (translated as The Wayward Daughter, for which read Saucy Little Stop-Out) is misleading: there is nothing hard to understand in this touching two-act romcom. The version by Frederick Ashton, now revived to mark its 50th birthday, is pure sunshine and pure Englishness – remarkable given its origins in France the month the Bastille fell.

Like all the earliest ballets, the original Fille fell out of use and out of memory. By 1960 all that remained were scraps of music by various hands, a bit of mime and an outline plot: girl loves boy, girl's mother thinks she could do better, girl wins out. Ashton's genius was to take those faded fragments and stitch them into a bright new fabric, interwoven with his own fondness for traditions, which happened to be English ones: Lancashire clogging, pantomime dames, maypoles and rainy picnics.

Performed with the right blend of exuberance and finesse, which seems to be the Royal Ballet norm just now, what's not to love? The sugar-averse may wish Ashton had done without the (real) Shetland pony and the dancing chickens (though it's impressive that Ashton's rooster was doing the John Cleese walk 20 years before John Cleese). But it would take a real curmudgeon to wish away the ribbon motif, which in Ashton's hands becomes the most ingeniously extended metaphor in dance. What begins as a single gesture – a girl tying a lover's knot to her boyfriend's staff – feeds into an ever more elaborate sequence of ribbon-craft. A mysteriously lengthening streamer becomes in turn a lasso, a skipping rope, horses' reins, a game of cat's cradle, a row of kisses written across the stage, and most magnificently, the spokes of a wheel, with the seraphically beaming heroine, Lise, revolving on one toe at its hub.

What stops this dangerously sweet confection from cloying is, partly, its cracking pace: many of the ensemble numbers overlap to give a sense of choreographic invention so profuse that it tumbles over itself to be seen. Another restraining element is the astute underplaying of comedy. Where Widow Simone – a male dancer in drag – could easily be grotesque, William Tuckett makes her adorable, a 6ft, mob-capped fusspot just as concerned that all her sunflowers should face the right way as that her only daughter should marry well. And on opening night when Daniel Capps, the conductor, threatened to launch into the clog dance music before Tuckett had donned his second clog, a wagging finger, directed at the pit, only added to the sense of spontaneous glee.

Carlos Acosta is a gift as Colas, given the radiance of his bearing, the precision of his solos, and the macho oomph that turns every jump into an amorous proposal. Not even Nureyev can have looked so fit in those yellow tights.

That up-for-it sensuality is matched, and more, by Marianela Nunez, whose fizzing technique makes the toughest test set by Ashton look like child's play. Executing a snaking backwards bourrée while stirring a bowl of porridge has to be the most extreme version of head-patting-tummy-rubbing anyone has come up with. She throws it off as if it were her daily wake-up routine.

Other casts (there are five in all) will bring other qualities to these roles, but the blast of friendly warmth from this national treasure is guaranteed.

In rep until 28 April (020-7304 4000)

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