Billy Bob Thornton, Union Chapel, London

A better class of roadie

"Boy, oh boy," whispers Billy Bob Thornton, surveying the scene in front of him, "This is somethin' else." The Victorian chapel is glowing with expectant faces, loud whooping noises keep erupting from the back, and people are climbing on to the pews to get a better view.

Not one to blend in with his surroundings, Thornton stands centre-stage in a sparkling bandanna, skin-tight jeans and biker boots, a big goofy grin spreading across his face. If he weren't a world-famous movie star, you might easily mistake him for a roadie.

Anyone who witnessed Keanu Reeves and his band Dogstar being pelted with junk food at Glastonbury will know how things can go horribly wrong when actors play at being rock stars. But Thornton isn't your average Hollywood have-a-go, having been in and out of bands since his teens. He once toured as part of Tres Hombres, a ZZ Top tribute band.

Now into his forties, and with a handful of critically acclaimed films under his belt, Thornton is finally taking his musical career seriously. Private Radio, a collection of country, blues and roots-rock songs, which was released earlier this year, was a credible enough debut, and there are two more albums in the pipeline.

While the music is hardly cutting edge, it's played by Thornton and his sizeable band with puppyish enthusiasm. Thornton is a decent singer, too, in his quieter moments echoing Johnny Cash. When the tempo is raised for the honky-tonk stomp of "Smoking in Bed", he even starts to sound like he's enjoying himself. The cover versions let things down, however – an earnest version of "California Dreamin'" by the Mamas and the Papas sends several punters scurrying to the bar in shame.

It may be curiosity that has brought people out this evening, but, even without his film-star status, Thornton has the vitality and colour of a rock hero. He strides confidently around the stage, slaps his fellow musicians on the back and spontaneously fills the gaps between songs with stories about his childhood and family. He tells us of his brother's journey from Houston to Philadelphia in pursuit of an absconded girlfriend; later we hear about Thornton's own drug addiction, agoraphobia and years of "living a lie".

The confessional nature of his conversation might be embarrassing were Thornton not such an engaging host. Happily, his enthusiasm is reciprocated. When he invites a few fans on stage to help him sing "Angelina", a tribute to his wife, the actress Angelina Jolie, the whole front row bounds up. Later on, one scallywag runs on stage, puts an arm around Thornton's shoulders and, camera in the other, takes a picture. Thornton is delighted and the crowd cheers.