My Morning Jacket, Shepherd's Bush Empire, London

My Morning Jacket's open-hearted innocence lets them get away with a lot. On one level a country stoner band, prone to good-time Southern boogie and jamming the Allman Brothers would approve, this long-haired Louisville, Kentucky quintet would have been laughed out of town not so long ago. Hipness isn't in their lexicon, the early 1970s don't seem to have ended in their heads, and interviews show a suspicion of everything outsider their own antique musical corner.

My Morning Jacket's open-hearted innocence lets them get away with a lot. On one level a country stoner band, prone to good-time Southern boogie and jamming the Allman Brothers would approve, this long-haired Louisville, Kentucky quintet would have been laughed out of town not so long ago. Hipness isn't in their lexicon, the early 1970s don't seem to have ended in their heads, and interviews show a suspicion of everything outsider their own antique musical corner.

But then, that's a lot of what's good about them too. On their latest, third album, It Still Moves especially, the spirits of early Neil Young, Brian Wilson, The Band, Lynyrd Skynyrd and Etta James still seem defiantly alive. Recorded in a barn on ex-guitarist Johnny Quaid's grandfather's farm, and centred round the reverb-drenched voice of band-leader Jim James, this is down-home music made without affectation.

Call it Americana or alt.country if it makes you feel better, but My Morning Jacket are a Southern U.S. rock band, of the kind the country's been turning out since Nixon was in the White House. As they prove tonight, though, they are a particularly good one. They welcome us in with "The Golden", a paean to the pleasures of a life on the road which has already seen founder-members Quaid and Danny Cash quit, so relentlessly do the band tour. This constant work has sharpened their playing to an extent most British bands can only imagine, and yet My Morning Jacket still retain a light-footed nimbleness about everything they do tonight, an adolescent joy far removed from the normal connotations of their stoner-jam sound.

Even the way the guitarists swing the well-shampooed locks which screen their anonymous faces has an infectious silliness. Their music, too, hit-and-miss on record, stays in a zone of gently mesmerising yet varied sensuality unlike anything I've heard in a while. Jim James' high, pure voice is shamelessly reverbed up to an Alps-bouncing level of echo - backing his belief that the effect equals "singing in heaven" - but its the subtler, less expected sounds which stay with me. On new song "Autopilot", acoustic guitar notes shiver like plucked harps, while elsewhere - in a show largely built from older and brand-new songs - quiet, slow-motion riffs take their time climaxing, and honkytonk piano rolls good-naturedly. The old skill they are reacquainting us with is the art of improvisation: not aimless jamming, but the ability to let music drift and settle, unlock your mind a bit, and yet never quite lose purpose.

For encore "Mahageetah", they sharpen up, throwing in stand-up soul organ and Southern boogie guitar for a climax in which every note vibrates powerfully. A knot of young fans reach out their arms for James as he bends to play for them. As with so much else about this band, he doesn't look vain, just friendly.