John Reilly And Friends, St Giles-in-the-Fields, London

He has an actor's confidence with funny, off the cuff chat, riffing on his discomfort with the music’s religious conservatism

“We’re not done with you yet,” booms the big man bounding up the aisle as support act Fionn Regan sings his last note.

John C. Reilly doesn’t only lose the “C” when not acting, but the crumpled intensity he has brought to even his comedy roles since making his name in Paul Thomas Anderson’s Boogie Nights (1997).

His sideline as a singer of the sort of old-time Americana T. Bone Burnett resurrected in the Oh Brother, Where Art Thou? soundtrack is plainly pure pleasure. It’s also a mission, shared with his friend Jack White, whose Third Man label has released singles by Reilly and tonight’s accomplices, Tom Brosseau and Lavender Diamond’s Becky Stark.

“The whole idea of this band is to keep old songs alive,” Reilly tells the unusually mature gig crowd drawn to the beautiful Soho church where William Blake worshipped.

In grey jacket, waistcoat and hat, Reilly has an old country singer’s semi-formal attire, and a strong, high croon to match. Brosseau and Stark, the former joining him on acoustic guitar, complete perfect harmonies. The songs mix 20 century country hits and more mysterious folk tunes with roots, Reilly acknowledges, winding back to the British Isles and as old as this church.

He has an actor’s confidence to hold us with funny, off the cuff chat, riffing on his discomfort with the music’s religious conservatism. The audience, too, laugh easily at the Damascene conversion on the way to the saloon in George Jones’s “Don’t Go”. Reilly does send up a prayer before a guitar solo, answered when he pulls it off. This personably comic tone leads us by the hand into old-time America’s wonders.

Ray Price’s “Heartaches by the Number” has country’s jet-black fatalism, Phil Ochs’s “There But for Fortune” a more hard-bitten sadness, from a more resistant tradition. The Carter Family’s “The Winding Stream”, taken by Stark and Brosseau while Reilly “wipes the flop-sweat from my brow”, is a waking dream quietly glorying in God’s nature, sung with the genre’s high lonesome sound.

There’s something pretty and peaceful in the entwined voices and acoustic guitar strums, the singers rising and sinking together on “Ain’t No Grave Can Hold My Body Down” (dedicated to Richard III), as the meditatively slow, soft sounds are carried on the church’s pure acoustics. The trio take a theatrical bow, humble mission accomplished.