ROYAL NIGHT OUT (12A, 97 mins)

Comedy/Drama/Romance. Sarah Gadon, Bel Powley, Jack Reynor, Rupert Everett, Emily Watson, Jack Laskey, Jack Gordon, Roger Allam, Ruth Sheen. Director: Julian Jarrold.Released: May 15 (UK & Ireland)

In this celebrity-obsessed age of 24-hour social media and omnipresent paparazzi, it's inconceivable that younger members of the royal family could mingle with us, the unwashed hoi polloi, without attracting attention.

Heirs to the throne would be engulfed by a sea of flashing smart phones, their every word regurgitated and scrutinised in 140 poorly punctuated characters.

Seventy years ago, Princess Elizabeth, the future Queen of England, and her sister Princess Margaret briefly escaped from Buckingham Palace to celebrate VE Day with the teeming crowds outside the royal residence.

They mingled with their subjects, completely incognito, as the people of London marked the end of the Second World War with an exuberant evening of revelry.

Screenwriters Trevor De Silva and Kevin Hood use this true event as the starting point for a heart-warming comedy of manners, which propels the two princesses on journeys of self-discovery in a capital awash with carnal desire and potential danger.

A Royal Night Out is frothy fun, embellishing fact with outlandish fiction under the jaunty direction of Julian Jarrold, who previously unbuttoned the stifled emotions of the era in the 2008 remake of Brideshead Revisited.

The film opens with archive footage of Winston Churchill announcing the end of the conflict with Germany.

Jubilant crowds gather outside Buckingham Palace where King George VI (Rupert Everett) is preparing a radio address with encouragement from Queen Elizabeth (Emily Watson).

Their daughters, Princess Elizabeth (Sarah Gadon) and Princess Margaret (Bel Powley), yearn to celebrate with the people but the Queen is resistant.

"We'll be walled up in this mausoleum for the rest of our lives," despairs Margaret. "I'm completely cheesed!"

Princess Elizabeth persuades her father to let them venture out for one night and the girls excitedly don their frocks, only to discover that their mother has arranged for two soldiers, Captain Pryce (Jack Laskey) and Lieutenant Burridge (Jack Gordon), to chaperone them at all times.

By chance, the princesses elude their escorts and head out into London on their own where Elizabeth finds an unlikely protector: a deserter called Jack (Jack Reynor), who isn't a fan of people of privilege.

"Family well-off by chance?" he asks, oblivious to his companion's true identity.

"We manage," replies Elizabeth tersely.

A Royal Night Out is timed perfectly to coincide with the 70th anniversary of VE Day and an air of wistful nostalgia blows through every frame of Jarrold's perky picture.

Gadon is luminous in a restrictive role, while Powley has considerably more fun as the rebel, who brandishes her superlative of choice - "wizard!" - with plummy gusto.

The script predominantly opts for laughter rather than lamentation, and is careful not to offend with a simmering romantic subplot between Elizabeth and Jack.

There's nothing here that will have the filmmakers entering the Tower Of London through Traitor's Gate.