Enjoyably rubbish from start to finish, this rollickingly silly account of Elizabeth and Margaret Windsor’s imagined Roman Holiday-style VE Day knees-up finds the young princesses at large on the streets of London in 1945, cavorting with prostitutes, hanging out with spivs (Roger Allam enjoying himself immensely), and scuttling amid the seedy dives of Soho.

Canadian Sarah Gadon is Lilibet (the sensible one), Bel Powley is Margaret (the drunk one), both giving their chinless chaperones the slip to embark upon separate adventures through the streets of London. While Mags (“I’m P2, no one cares what I do!”) is swept off her feet by a champers-swilling cad, Liz bonds with sensitive awol squaddie Jack (Jack Reynor), whose anti-monarchist angst soon crumbles to reveal a barely hidden heart of gold.

The whole thing is as fake and fragile as a cheap commemorative mug, but there’s ripe fun to be had in its tickety-boo trashiness. Ideally viewed on a chocolate-fuelled double-bill with William & Kate: The Movie.