Alasdair Roberts and Emily Portman

She has a relentless chirpiness, most obvious during her attempt to get the audience to sing along to Old Mother Reeve, which adds a delightful incongruity to her catalogue of witchy songs inspired by Greek mythology, Angela Carter novels and fairy tales.

The peculiarly English darkness of the Glastonbury singer's material initially puts one in mind of Mary Hampton, especially on Stick Stock.

Based on a metronomically plucked cello and vocal rounds from Portman and her
backing band The Two Lucys, she creates a sense of suspense that gradually builds to a gruesome close.

But elsewhere the oddness is pitched within a less experimental folk vein.

Traditional song Hollen has aspects of Jackie Oates, with Portman swapping concertina for ukulele, while the references to vodka and nightclubs on Hinge Of The Year have echoes of Eliza Carthy.

A carnivalesque number that features viola player Lucy Farrell on a musical saw, it brings a modernist touch to an otherwise timeless set.

The only false note here is her "mother-to-son" duet with headliner Alasdair
Roberts.

It is, she explains, the first time they've performed it live and it shows — her fluting vocals and his lugubrious burr are strangely mismatched, with both of them slightly out of sync on key phrases.

As if to avoid a repeat of such incompatibility, Roberts's own set is largely performed solo and acoustic.

It's an approach that focuses attention on the Glasgow-based singer's intimate vocals and nimble guitar playing, aided by fingers so spindly they make Jimi Hendrix's resemble sausage rolls.

At the forefront of the folk revival, he's an in-demand collaborator with the likes of Will Oldham and Mairi Morrison, with whom he's about to release a new album.

But as a live performer, he suffers from a sense of hunch-shouldered unease that undermines opening number The Dun Broon Bride and the sublime rumination of mortality that is Waxwing.

It's an awkwardness that's apparent even when he's given moral support by The Two Lucys, who provide "an experimental string section" on Gave The Green Blessing.

It's therefore slightly ironic that the set's stand-out moment comes when he performs an acapella version of The Cruel Mother.

Hands flexing at his sides, he howls the words with such conviction that he erases any sense of disappointment with the rest of the set and seals his reputation as being one of the country's finest folk singers.

Both singers are touring Britain in April and May. For details, visit:
www.alasdairroberts.com and www.emilyportman.co.uk