Cerys Matthews, Concorde 2, Brighton

If absence makes the heart grow fonder, a nervous breakdown and a spell in rehab clearly makes it full to bursting. Matthews looks wide-eyed and overwhelmed at the loud whoops and whistles that erupt when she appears on stage. "Ceerrrease," wails the audience. "We love you." "Thank you", she replies shyly, "It's nice to be back." This is Matthews's first UK tour since the ignominious demise of her band Catatonia. Where the majority of Britpop bands seemed to simply run out of steam, the Welsh band hit the wall at full throttle, buckling under the weight of personal frictions and Matthews's legendarily excessive lifestyle. In 2001, amid rumours of mental collapse and alcohol addiction, the singer disappeared out of sight. A year later, she appeared in Nashville where she met and married her husband, the producer Seth Riddle. It was there, in a country shack a few miles out of town, that she recorded Cockahoop, a breathtaking collection of old and new folk songs which form the backbone of tonight's set.

She certainly looks different. In Catatonia, Matthews habitually appeared on stage clutching a bottle of Chardonnay. Now she arrives with a bottle of water in her hand and a discernible swell around her belly. She sounds different too. Gone are the caterwauling choruses and tumultuous guitars that catapulted Catatonia to the top of the charts in the mid-Nineties. Against the more subtle sounds of mandolin, fiddle, pedal steel and acoustic guitar Matthews's voice is transformed. It crackles and fizzes like a firework, and reaches dizzying emotional heights. It's as if she's learned to sing all over again.

If the crowd are expecting to hear old hits they're too polite to say so; happily, the singer's new-found direction seems to sit just as comfortably with her fans. If there's any irony intended in "Chardonnay", a raucous love-letter to her favourite drink, she's not giving anything away. A handful of songs bring echoes of the old Cerys - the bawdy, bar-room stomp of "If You're Lookin' for Love" ("Baby just go and set yourself free/ But if you're lookin' for love come see about me") and "The Good in Goodbye", a scorching paean to lost love, proves that she can still belt'em out when she wants to. But it's during the sleepy, sombre tracks that Matthews is in her element. "Caught in the Middle", one of several songs on Cockahoop penned by Matthews herself, is full of love and longing while "Weightless Again", a cover of the Handsome Family's ode to suicide ("That's why people OD on pills/ And jump from the Golden Gate Bridge") is wonderfully dark, bringing to mind dust, tumbleweeds and similar Lynchian motifs. "All My Trials", another darkly suicidal ditty previously recorded by Harry Belafonte and Joan Baez, is sung at a whisper and immediately brings a lump to the throat. With an array of stringed instruments, Matthews's backing band, which includes her producer and one-time slide guitarist for Bob Dylan, Bucky Baxter, provides a resolutely old-fashioned framework for her songs, leaving her vocals to take centre stage.

This isn't so much reinvention as Matthews going back to her roots. When she was a child, her grandmother introduced her to old Welsh folk songs which made their way to the Appalachians via European immigrants in the 19th century. Now Matthews believes she is reclaiming her heritage. As she sings the old Welsh hymn "Arglwydd Dyma Fi", which roughly translates as "Lord, here I am", she radiates tenderness and warmth. Less a cynical overhaul, this is the sound of a singer who has finally found her voice.

Cerys Matthews plays London Union Chapel on 19 June; Cambridge Junction on 24 June; Manchester University on 25 June and Glastonbury Acoustic Stage on 29 June