I'm due to meet him in a Russian tea room in Primrose Hill, but find the man instead in the local wine shop, pondering the chiller cabinet. Across the road, there's a café crowded with a half dozen pavement-cramming prams. He makes a joke about fertility cults – you could say he was the centre of one, once – and chooses another café, on the sunny side of the street.
With his straggly hair pulled back, a goatee and a family of well-lived in wrinkles marking out several lifetimes, there's nothing plastic about Robert Plant; he has lived fully through several reincarnations, from midlands Beatnik to new Yardbirds singer, priapic 1970s rock god, 1980s survivor, 1990s reviver, and in the last decade, evoking rootsy Americana with 2007's hugely successful Raising Sand with Alison Krauss and the recent Band of Joy project with Buddy Miller and co-vocalist Patty Griffin, to whom he is rumoured to have married. "I eloped and ran off to Texas," is all he'll say, "So now I spend half my time there and half here." There, he lives in what he describes as 'an old crack house in Austin', a rented place infested with termites. "I tap my hand on the table and they fly out the walls in this huge cloud, like something from a Disney film."
Band of Joy was Plant's first band in the 1960s, and it's joy, rather than legacy that his next project is all about, for with The Sensational Space Shifters, Plant, with Griffin and a fresh band of brothers, including JuJu's Justin Adams and Juldeh Camara, and ex-members of Portishead, Cast and Massive Attack, will close Womad's 30th year, with Khaled, Jimmy Cliff and Femi Kuti among the line-up.
"I've been lucky to meet some really stimulating people, and Justin is the key to so many doors," enthuses Plant. "But sadly, in the life I led" – within Led Zeppelin, he means – "it was a closed circle, and I suppose it was because everyone was much younger and there was a competitive aspect. And I'd missed that; the revelry has only come in the last 10 years".
The Led Zeppelin reunion is only five years gone, but are those days of being a rock god further away for him than for the band's listeners? "Absolutely!" he cries. "When you're a big fish in a small pond, way back when, we were better than anyone around us, then suddenly we're playing with doyens of the time. There was such charisma and mood at the festivals in America. You had to really dig in. It was quite an experience – and there was Janis Joplin to give you a tincture for your throat afterwards. It was pretty overwhelming and very exciting, but yes, it was a long way from here."
These days, Plant plays his game with a different stack of cards. "You can grow or you can get so far that you seize up and say, 'this is it, this is my fate, I'm staying with it'. Stick or twist like blackjack." Which must have been the cards he was dealt around the Led Zep reunion at the O2. So what if 20 million fans applied for tickets – Plant wouldn't stick, and there was to be no Zeppelin tour.
Plant's winning hand – this sense of finding a new music that refreshes those parts the back catalogue can't reach – has its roots in his elopement to Texas. "I made Raising Sand just before the Zeppelin O2 gig and this new dawn, if you like, gave me a whole new view of music and musicians and application and joy – because it didn't have any of the Sixties-Seventies hangover in it. The last vestige of pin-up had gone. I was working with people who were steeped in their stuff, Appalachian, whatever it may be. They'd made that choice as to where they wanted to go. It was a new dawn, entirely, for me. It trickled through and Buddy Miller and I created Band of Joy, which was tougher than Raising Sand. And we've recorded a new record that's far, far out with psychedelic pedal steel and all sorts of stuff."
And with the Space Shifters, Plant is pushing the boat out even further. "It has eight people in it now, it's like a review," he grins. "It's so joyous and the great thing is that it's not a precious metal at all. People come together to do what they want to do, and what they can. The sound Justin and Juldeh make melds into one beautiful thing. The space-shifting is a natural movement. It's wild, and to stand back in the middle of it, especially with Patty singing alongside me, she looks at me and raises her eyebrows as if to say, 'this doesn't happen in Texas'."
To limber up for Womad, the Space Shifters are testing their abilities at the HMV Forum tomorrow. "And what is it really, but people who can do what they do, allowing other people to join in? The exchange is there." That little chuckle again. "I can't believe my luck. It could have been so different." Quieter, more to himself: "Fuckin' murder."
That's not to say he's wiped the past from his repertoire. Far from it; it's just that he'll turn it inside out. "We could switch to bendirs and go off into some Arabic folk song in the middle of 'Whole Lotta Love'," he says. "I take chances and I risk, but I don't study. I'm trying it on. With this spacey, trippy shit, I get in the middle of it and go."
Letting go has been his working method since the beginning, along with a passion for the roots of rock '*' roll in the Blues, and beyond, in African music. "In 1972," he remembers, "I took Jimmy Page to this part of Morocco called the sub-Sahara, between the Atlas Mountains, and when you go into the market and start buying cassettes, you're listening to the lone voice, the one bandir and the violin. The Berbers and hill tribes –what was left of the tribes of the Lords of the Atlas – were making this music that was eternal. Jimmy and I took a tape machine, recording people on our way. While at the same time still being Led Zeppelin."
Some 40 years on from those field trips, Plant will revisit the music of the Atlas – as well as the roots music of Gambia, Mississippi, and Appalachia, when he hits the stage and lets it all go at Womad. With that voice peeling into the night air around the festival grounds and the band pushing, grinding and shapeshifting around him, you may be forgiven for imagining yourself back on some free festival field of the early Seventies, at the apogee of the Zeppelin live experience.
"It was a bit overcooked at times," he admits, "and a bit self indulgent but it was part of the times and actually, back in the Sixties and Seventies, people played great, and why not extend it, why not enjoy it? It's what the quality and the psyche of the audience in those days demanded. It did go on and on but no one was looking at their shoes while they were playing. It was like, 'this is fucking great; excuse me, I'm gonna be a while'."
With the second Band of Joy album due for release next year, it's down to the Space Shifters to keep Plant testing his boundaries as a solo artist. "So long as it feels good, that's what matters, really. I'm not trying to break the bank and I'm certainly not trying to play Wembley Stadium," he laughs, adding quietly, almost matter-of-fact, "though I do know how to do that." He laughs again, and shoots an impish, well-weathered look, as if considering, once again, the roots of it all. "I was the guy who replaced Keith Relf in the Yardbirds," he says, almost in wonder, "with a voice that fitted with the time." That grin again. "Now I'm all ears."
The Sensational Space Shifters play the HMV Forum, London, tomorrow. The 30th Womad from 27-29 July at Charlton Park, Malmsbury, Wiltshire, with tickets £25-£135, and headliners including Robert Plant and Orquesta Buena Vista Social Club.