They say Christmas is for families, and in recent years the Wainwright/McGarrigle New York Christmas concert has become an institution, with singing siblings Rufus and Martha Wainwright and their folk-icon mother Kate McGarrigle being joined by aunties, cousins and celebrity friends for a knees-up at Carnegie Hall.

The famously dysfunctional clan – augmented by Kate's sister and musical partner Anna – have this year transferred to London for an event that might be expected to yield more than its fair share of festive family tensions. "You don't want to see backstage," warn French and Saunders, opening the evening. "There are rivers of blood back there."

Yet this proves a happily harmonious family summit from the moment that new mother Martha, in six-inch heels, clunks on to trill the Waitresses's 1981 novelty hit Christmas Wrapping. Rufus, for his part, is a reliably waspish MC and pours a magnificently overwrought vocal over Christmas Is for Kids, while the McGarrigle sisters' ghostly harmonies are delicious on Cherry Tree Carol.

Elbow's Guy Garvey, looking positively Dickensian, drops by for a moving version of Joni Mitchell's River, before a pink-Stetson-sporting Boy George delivers a rather less essential cod-reggae take on White Christmas. Yet both are upstaged by Ed Harcourt and Martha Wainwright's rollicking take on Fairytale of New York.

Rufus welcomes his German partner Jörn Weisbrodt to the stage with a kiss ("Churchill would be rolling in his grave!"), and the pair serenade the crowd with Silent Night. The evening climaxes with a huge sing-along of John and Yoko's Happy Xmas (War Is Over), then the Wainwright siblings and their mother encore with In the Bleak Midwinter. Remarkably, they make even this sound rococo.