They split the hall in half; the left side to sing along with Belinda and the right side to sing along with Heidi. One half goes "Behind their backs she's Gentlemen Jack" while the other half goes "She's Gentlemen Jack behind their backs" and so on, while the music on the stage gets wilder and more raucous. We are supposed to keep the chant up as a counter melody as Belinda and Heidi go into the last verse. "The code is cracked, your bags are packed /The knives are out for Gentleman Jack."
When O'Hooley and Tidow first played Bristol, they say, less than 30 people turned up, mostly to hear the support act. (I don't think I was at that gig, but I did hear them open for the mighty Chumbawamba before they were famous.) But since then Gentleman Jack has been plucked off the Fragile album by the BBC and used as the theme tune for the prestige historical docudrama about Anne Lister. As a result, their present tour is completely sold out. They are calling it the #Gentleman Jack tour. "Not that we're milking it."
Fame has not spoiled them: it is very much business as usual. Their act is not easy to describe: I understand where the "chamber folk" designation comes from, although I would be hard pushed to say what it means.
They do narrative songs, cleverly based on historical figures they've heard about. When the BBC are finished with Anne Lister they could do worse than make a series about women's cycle champion Beryl Burton for whom the duo have already written a theme song. ("Born into nothing / a shy awkward lass / Coordination?/ St Vitus her dance"). But they also do songs about real-life stories they have come across like the elderly lady who takes a local tramp in at Christmas and learns about his life story. ("Breaking of bread and drinking wine / For once he had a shared communion / Chose to spend her Christmas time /With someone viewed as barely human")
Belinda gets out her accordion for the traditional folk sing-a-long "All for me grog" and we even get an acapella version of something by a young people's band called Massive Attack. There are close harmonies, driving rhythms and a jokey, naughty, stage rapport. The audience can't help laughing at the unexpected pauses in Beryl. But a lot of the songs are heartbreakingly sentimental. There's a lullaby sung by a mother to the child taken away in the 1960s child migration programme and a true story about a home for orphaned elephants.
They normally do Gentleman Jack at the end of the first half, but tonight they hold it back for the encore. ("We'll just sing this ditty.") It isn't the regular St George's folk crowd: it's lovely to be with an audience who have clearly come out specially to hear this band, and this song. The atmosphere is humming. It's taken them a decade to be overnight successes and they totally deserve it.