Kathryn Williams & Neill Maccoll, Komedia, Brighton

The first time Mercury nominee Kathryn Williams and guitarist and producer Neill MacColl met, in 2005, she sang a Vashti Bunyan song and cracked a dreadful joke. The second time, the following year, they performed "The First Time Ever I Saw Your Face", the standard forever associated with MacColl's parents, folk singers Ewan MacColl and Peggy Seeger. The third time, Williams and MacColl wrote 22 songs together in a week, half of which form the duo's wonderfully delicate album, Two.

On the opening night of their British tour, the two singers show that their partnership is still growing and developing beyond expectations. They feel their way in with the vignette-like "All" and the gentle melody of "Weather Forever", before revisiting "Stood" from Little Black Numbers.

A venue such as the Komedia in Brighton fits Williams and MacColl to a tee as she thanks the fans who brought her a raspberry cake. Motherhood helped Williams conquer her stage fright and she makes fun of her sidekick's muso tendencies and tells an unrepeatable onanist joke. The self- effacing MacColl proves he can be a fine singer with a cover of Tom Waits's "Innocent When You Dream".

Just when things are about to get too coffee-table cosy, Williams subtly alters the blissful mood of "Blue Fields" by mentioning "selfish people", swears during "Armchair", and switches point of view in the pointillist "Frame". She is a painter, too – "a bad one," she claims – and she's forever adding little touches of colour with MacColl's arpeggios providing light and shade. But it's the unsettling, confessional "Grey Goes" that really proves the centrepiece when Williams loops her vocal lines again and again like an air-traffic controller stacking planes. She tops it all by getting a bow out and using it to play her acoustic guitar. Eat your heart out, Jimmy Page.

"Come with Me" is more what you'd expect from Williams but only happened because MacColl encouraged her to persevere and actually dare to use the word "darling". Their telepathic understanding and vocal blend are breathtaking. They draw the best out of each other and end with the exquisitely detailed "Holes in Your Life". Williams delivers deep, cutting insights with an occasional giggle. As her voice soars and roars at the end of an arresting version of Leonard Cohen's "Hallelujah", the hushed reverence is palpable.

Touring to 19 April ( www.williamsmaccoll.com)