Politically speaking, this may be as totemic a film as The Full Monty was in 1997. Another from this year’s pretty rote heritage-cinema crop, Julian Jarrold’s costume romp takes the much-chewed titbit about the young Princesses Margaret and Elizabeth being let out of Buck House for a few hours on VE night as the basis for an essentially silly, trivial runaround. The result is 50% flagwaving, stocking its replica Trafalgar Square with by-the-yard bunting and extras, and 50% galumphing big-band score, with a brass section that parps breathlessly whenever we’re meant to find something amusing.

Professional chaperone Jarrold lends it more mildness than wildness, his safe hands forever muffling any danger or sexiness. Where previous dusk-till-dawn narratives have wielded their timeframe as an index of change, here everything stays the same. Bel Powley’s Margaret remains resolute in her jolly-hockey-sticks snorting, while respectful supposition ensures Lilibet (Sarah Gadon, labouring to turn all her “off” into “orf”s) goes no further than Barnes with her disgruntled soldier consort. It’s a thin, trickledown sort of fun, broadly comparable to spending the afternoon in a mocked-up Lyons Corner House: the barrel is dutifully rolled out, but its contents prove no more intoxicating than ginger beer.