Rufus Wainwright says that he’s been rehearsing these back-to-back orchestral presentations of Want One and Want Two for three days, “and I feel like I’m on a different planet” – the Canadian singer-songwriter may well have been dreaming about them for 20 years. Rock artists who enlist an orchestra can sometimes resemble that meme of Winnie the Pooh in a bow tie and monocle – a clumsy grab at classiness – but then the Want albums aren’t really rock. Drawing on chamber-pop, cabaret, opera and the Great American Songbook, with knowing quotations from Ravel and Wagner, these songs were built for opulence. The BBC Concert Orchestra, conducted by Sarah Hicks and joined by original drummer Matt Johnson, performs the work of several arrangers, each one a sensitive translation. As Wainwright hops between grand piano and acoustic guitar, they know when to roar and when to whisper. “I’m 50! Jesus!” Wainwright exclaims at one point, conscious that he is reinhabiting the turbulence of his late 20s. Dressed as if for a travelling circus, or a scene-stealing turn in The Last Waltz, he looks splendid and sounds better, notwithstanding a couple of ragged false starts, charmingly handled. Like many cult artists, he makes a virtue of his fallibility. “Please stay to see if I make it or not,” he says at the end of Want One. “It’s kind of like a sporting event.” For Want Two, the hour is later, the hall a little emptier, the songs a little patchier. Guest vocalist Jake Shears gives it everything he’s got but Old Whore’s Diet – nine minutes long and you feel every one – is a rare duffer. The magnificent encore of Bush-era protest song Going to a Town (which closes both shows) is a welcome corrective. That aside, these albums are Wainwright’s twin peaks as a songwriter, praised at the time by David Bowie and Elton John. The range is extraordinary: the quietly patricidal Dinner at Eight, Memphis Skyline’s shimmering tribute to Jeff Buckley, the wracked immensity of Go or Go Ahead. For all its musical grandeur, one of the night’s biggest ovations goes to The Art Teacher: just Wainwright, a piano and a perfect song.