Stephen Frears' new film is based on a true story, but one of the biggest compliments it can be paid is that you wouldn't know it. Florence Foster Jenkins feels less like a biopic than a classic postwar studio comedy - a pillowy paean to silliness, and the perfect antidote for sobering times.That's particularly appropriate given its subject: an American amateur opera singer whose voice brought joy to millions in the depths of wartime, largely because she could turn even the most graceful coloratura soprano line into what could only be described as a contaminated aria.Foster Jenkins wasn't famous because her singing sounded like a cat fighting a duck in a wheelie bin, but because she committed to it with the panache and depth of feeling of a peak-form Callas. Her records became instant collectors' items, and her concerts sold out immediately.Frears turns Foster Jenkins's story into an Emperor's New Clothes fable in reverse, in which everyone clocks exactly what's going on, but realises that shouting out would only spoil the fun. It follows Florence (Meryl Streep) in late middle age as she approaches that life-capping Carnegie Hall gig, chivvied along by St Clair Bayfield (Hugh Grant), a modestly talented actor and her doting second husband.Streep plays Florence as a seamless hybrid of dumpy arts-scene doyenne and excited schoolgirl: when she performs, she draws her elbows in close to her chest and occasionally twists very slightly from side to side, like the primary school choir girl finally getting her spotlight moment.And it's pure Streep soufflé - free from the weighty responsibility to imitate (as in The Iron Lady) or emote the house down (as in August: Osage County), she gives her most human performance since Nancy Meyers's 2009 romantic comedy It's Complicated - full of warmth that gives way to heart-pinching pathos.But Florence isn't the film's centre of gravity. That duty falls to St Clair, who treats her with a kind of grandfatherly affection, while shielding her from the odd sling or arrow that makes it over the ramparts. For those of us who felt Grant was born half a century too late for the career he deserved, Florence Foster Jenkins will come as partial vindication.He's on preposterously good form here, gliding through every scene with a lightness and wit that's completely '50s, and perfectly in keeping with the film's moreish, brandy-butter aesthetic.The couple's relationship is snuggly but sexless: when Florence says "I love you", St Clair's reply (which Grant somehow makes sweet) is: "Mmmm. With all the knobs on." But she sleeps alone, and St Clair keeps an apartment with mistress Kathleen (Rebecca Ferguson).Florence's rehearsal scenes have a gently escalating ludicrousness about them that's totally winning, and a sequence in which she ends up being grabbed from behind by her vocal coach (David Haig) and all but ridden into tune, is a snort-inducing comic vignette.This is a delicious, finger-tingling comedy about the creative instinct that makes your heart want to squawk with joy. ..