4/5 stars Based on a scarcely believable true story, John Madden’s Operation Mincemeat is a stately World War II drama set at a vital turning point in the conflict. The year is 1943 and Allied forces (those opposing Germany, Japan and Italy) plan to storm the strategically located island of Sicily in the Mediterranean, which is exactly what German intelligence is expecting. A ruse is cooked up by British secret agent Charles Cholmondeley (Matthew Macfadyen) to convince the Nazi high command that the Allies are massing to invade Greece, a sleight of hand that will leave Sicily largely unguarded. Cholmondeley is joined by naval representative Ewen Montagu (Colin Firth), since fundamental to the plan is disguising a corpse as that of a dead British marine – one who happens to be carrying documents confirming this fake Greek raid. When the body gets washed up, the trail of deception can begin. As ludicrous as it sounds – and as Jason Isaacs’ naval intelligence director thinks it is – that’s the plan put into operation. It’s one that’s not without its ethical concerns – not least the real identity of the corpse that’s being used. Coincidentally, Operation Mincemeat has just been turned into a comic musical that debuts in London’s West End this month; Madden’s film takes a more sombre approach. Simon Russell Beale prowls the corridors of Westminster as Winston Churchill in typically imposing form, while Mark Gatiss pops up as Montagu’s brother Ivor, whose suspected ties to the Communist Party cause internal strife. Less successful, perhaps, is the love story between Montagu and an MI5 secret service clerk, played by the ever dependable Kelly Macdonald. There is at least time for a wry in-joke amid all this high-calibre espionage. Johnny Flynn plays a young Ian Fleming, clacking away at his typewriter in MI5’s offices some nine years before the publication of his first James Bond novel, Casino Royale . Madden keeps it all ticking over efficiently; no stranger to the genre – his 2010 film The Debt dealt with Mossad agents apprehending a Nazi war criminal – he confidently marshals the estimable British ensemble cast and maintains the tension. Of the cast members, a mustachioed Macfadyen comes out top. An actor at the peak of his powers following his recent work in Succession as the odious social climber Tom Wambsgans, he comfortably inhabits his role here as a shy, ex-military man with the brains to think outside the box. In the end, it’s the sheer nerve of the operation – crystallised by that all-too-silly code name – that will keep you hooked. Want more articles like this? Follow SCMP Film on Facebook