Paloma Faith and the Guy Barker Orchestra, Jazz Festival, Cheltenham Gregory Porter featuring Jamie Cullum, Jazz Festival, Cheltenham

Jamie is swinging his hammer on the chain gang – but Mrs Overall just swings

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Two years ago, Paloma Faith and Guy Barker closed the Cheltenham Jazz Festival with an evening of lovelorn torch songs, Down at the End of Lonely Street. On her return engagement, Faith chose to debut the whole of her soon-to-be-released second album as the festival's first Artist in Residence, which also involved her booking (and duetting with) the veteran soul singer Candi Staton, and programming a pop-up cinema. If the 2010 performance had been a rousing if slightly nervy triumph, this time it was sensational. The venue was a hit, too – a circus Big Top, replacing the sonically challenged Town Hall – and Barker's superb arrangements for the 48-piece band created a jazzier, funkier and poppier sound that made the upbeat repertoire really swing and swoosh, aided by a sassy female backing trio.

Though the unfamiliarity of the material made this a tough gig ("I'm so pleased you haven't been able to buy the album yet," she said, "because then you'd know what a terrible mess I just made of that last number"), Faith proved herself a star. This was partly due to her soulful voice, but mostly to her winning stage presence: streetwise Cockney waif done up as Forties jazz vamp, with any pretensions undercut by the comic timing of what might be termed her Mrs Overall persona, whose asides to the audience suggest that the whole edifice is about to come crashing down on her head. The songs from the new album, Fall to Grace, (co-written by Faith with several collaborators) are impressively hook-laden, but the real treats came when she mixed them with cover versions of soul classics such as Bettye LaVette's "Let Me Down Easy". Near the end, when she sang "I'd Rather Go Blind" by Etta James ("the woman who taught me how to sing"), it was pure soul heaven, Faith's voice moaning the crucial three repetitions of "I was just ...". Not many women from Stoke Newington can do that and win.

If Paloma Faith's voice is almost entirely self-willed, the US jazz/soul vocalist Gregory Porter has both nature and nurture on his side. His mother was a church minister in Bakersfield, and he began his professional career in musical theatre, writing and performing a one-man show about lost father-figures, Nat King Cole and Me. He's also a big man, with big lungs to match, but what really impresses about Porter's voice is its hinterland: there is so much power in reserve that he needs only to let out a little at a time to convince. His orotund phrasing and warm, Californian intonation complete a fabulous vocal talent. But Porter is no mere canary: he writes the songs he sings, with a strong suit in dreamily spiritual, black-consciousness lyrics.

The role of Jamie Cullum – an icon both of the festival, for which he is guest director, and of Radio 2 – was more problematic. He introduced Porter, sang a couple of duets, played a bit of piano, did a vocal feature himself and was every bit as engaging and likeable as he always is. But if you knew Porter's two excellent albums already, you eventually wanted Jamie to buzz off so we could hear a bit more of them. And when, in a duet on Nat Adderley's "Work Song", Jamie sang: "I been breaking rocks on the chain gang", you couldn't really believe him, could you? His generous sponsorship worked, however: next year, Gregory Porter will easily fill the Big Top himself.

'Fall to Grace' by Paloma Faith is released on 28 May. She plays G-A-Y Heaven, London (0844 847 2351) on 26 May. Gregory Porter plays Band on the Wall, Manchester (0161-834 1786) 12 Jun, and Bloomsbury Theatre, London (020-7388 8822) 13 &14 Jun