Some wag once asked whether The Godfather was like watching This Is Spinal Tap for real-life Mafiosi. One wonders if the British monarchy would have similar feelings sitting through Julian Jarrold's A Royal Night Out, a Cinderellaesque race against time (there's even a broken shoe) that uses the old "inspired by true events" chestnut.
In this case the facts are that teenage princesses Elizabeth (played here by Gadon) and Margaret (Powley) really were given a pass from the Palace to join in the VE Night celebrations in London on May 8, 1945. They danced a conga in the Ritz, mixed with their subjects in Piccadilly and heard their father's speech from the other side of the railings on the Mall.
In Jarrold's parallel universe Margaret goes missing and there's a chance and coincidence-filled cross-city search to find her, with a bolshie young airman called Jack (Reynor), visits to pubs and 'clubs', spivs, punch-ups and even the slight sniff of romance en route.
While the story makes Game of Thrones feel like a documentary, Jarrold deftly directs the chalk-and-cheese dynamic between Gadon and Reynor, the pacing is good and the production design excellent, with the recreation of the night in question suitably vivid and surprisingly poignant. It's no Brief Encounter or Ealing-equalling escapade, but there's enough here for teenagers, the over-80s and anyone in between to join in the fun.
Indeed, the only bad taste left by this enjoyably daft caper is the reduction of Margaret - then aged 14 - to some ditsy, tipsy caricature in a bid for laughs and to stress her sister's leadership qualities.
Too much perspective, as a member of a very different kind of royalty might politely say.
Harry Guerin