Tony Benn & Roy Bailey, Komedia, Brighton; Xiu Xiu, Fleece & Firkin, Bristol

In the week when Mumford & Sons have been performing at the White House as David Cameron's pet poodles, a night spent reconnecting with folk music's true radical roots couldn't be more timely. I just didn't expect it to happen with the help of a former cabinet minister.

Tony Benn and Roy Bailey have been performing their Writing on the Wall show on and off for two decades, and in 2003 it won them Best Live Act at the BBC Radio 2 Folk Awards. At 86 and 76 respectively, Bailey is entitled to turn to Benn and quip: "We are a live act, aren't we? Just ..."

It's the politician, not the singer, who is the more recognisable figure, and when Benn receives rapturous applause upon taking a stage on to which Bailey has already ambled, the latter has a mock-disgruntled grumble to the effect that "You didn't clap when I came on ...".

Bailey, however, is no lightweight: this is a man who received an MBE for services to folk music, only to return it in protest against UK foreign policy on Palestine and Lebanon.

Over two hours of songs and stories, the pair present "a history of this country seen from bottom-up, not top-down", with Benn aiming to kindle the "two flames" he, ever the optimist, believes are burning in the human heart: "the flame of anger against injustice and the flame of hope that you can build a better world".

The interplay between the pair of them is hilarious, with one often unsure what the other is doing: there's laughter after Benn ends a bit about Greenham Common by turning to Bailey and saying: "And maybe now you'll sing a song about peace, or whatever."

Topics leap across the centuries, often drawing unseen connections, from the Black Death to Occupy London, from the Levellers and the Diggers ("the first socialists") to the English revolution (Benn won't call it the civil war). He's a compelling speaker, whether telling tales of his life in politics or quoting sources from Oscar Wilde's The Soul of Man under Socialism.

As well as his own material, Bailey, a rousing and powerful singer, tackles songs from the folk tradition and even ones he found accidentally on Google. Perhaps most moving is "World Turned Upside Down", the Diggers anthem (via his collaborator Leon Rosselson), of which he pretend-snarls "I didn't get it from Billy Bragg, and I didn't get it from Dick Gaughan ...". It contains a verse which encapsulates the mood of this inspiring night: "The sin of property/We do disdain/No one has any right to buy and sell/The earth for private gain."

"This is a ridiculous show, isn't it?" Bailey muses from his stool as Benn sits in an armchair. "Two decrepit old men, we have to be winched onto the stage. Talk about Morecambe and Wise ... although I'm not sure who's who."

Shock tactics are easy. It takes intellectual bravery to have a point, and to make that bloody imagery resonate with emotional truth. Xiu Xiu, the Californian band whose name sounds like a randy panda in a crate, have a number called "Support our Troops", which begins with the words "Did you know you are going to shoot off the top of a four-year-old girl's head, and look across her car seat, down into her skull and see into her throat?"

Their latest album, Always, is dominated by falsetto-voiced electropop tunes about gay sex and murder, but do not be fooled into thinking of them as a mere Bronski Beat. The reality is far more challenging. Most extraordinary is "Fabulous Muscles", a brutal depiction of masochistic gay love. Performed drumless to a hushed audience, it contains couplets such as "Cremate me after you cum on my lips/Honey boy, place my ashes in a vase beneath your workout bench".

Music Choice

As John Lydon reactivates his newer version of Public Image Ltd, original PiL members Jah Wobble, right, and Keith Levene offer their own take on the classic Metal Box album at the Trades Club, Hebden Bridge (Fri) and Ruby Lounge, Manchester (Sat). Meanwhile, enigmatic Mancunian growl-rockers WU LYF play Heaven, London (Wed, Thu).