“David, how are you?”

“Er, Bryan.”

“No, I’m Robert. Carmen, this is David.”

Somewhat tersely: “Bryan, actually.” “No, Robert — anyway, how are you?”

The cafe is startled to a halt by my explosion of laughter. Talk about making plain your relative places in the rock’n’roll hierarchy. Plant, who is here to discuss a new album, affects mortification, but he is not fooling anybody. Both this anecdote and the album tell an interesting story about the British generation that re-invented rock’n’roll and in whose shadow the rest of us have lived ever since. We are talking about the baby-boomers: the ones whose parents survived the carnage of the war, then presided over the most spectacular period of economic expansion the world has ever seen. To the boomers, the newly secure world of their parents looked dull and joyless, so many of them rejected it.

The fascinating thing, though, is that so many of the Brit boomers should have chosen American blues and R&B music as their means of escape. Their enthusiasm fostered in art schools that would previously have been accessible only to a privileged elite, these kids ultimately turned themselves into all or part of the Beatles, Stones, Who, Yardbirds, Animals, Kinks, Cream, Fleetwood Mac, Derek and the Dominos, the Hendrix Experience, Velvet Underground, Faces/Small Faces, Led Zeppelin, Deep Purple, Elton John, Pink Floyd, Free... The further we get from that period, the more bizarre the list begins to look. One little-known feature of the beat boom — which became the British invasion of America — is that, when the Brits took up the rock mantle, American rock’n’roll had been deserted by its vibrant founders (Little Richard, Jerry Lee Lewis, Chuck Berry, Elvis) and seemed to be dying.

The story does not end there, though, because these gilded boomers are supposed to be fading away by now. But they are not. They still want to run the show — and are running it. Not only do they dominate politics and pretty much everything else, they are still rocking into the night, and way beyond a sensible bedtime for people of their advanced years. Look at Bowie and the Stones, both of whom have won plaudits this year. And here, sitting opposite me, more jowly than he once was, but funny and voluble and enthusiastic, is Robert Plant, with a hot young band and an album that unintentionally explains some of this stuff. Sixty Six to Timbuktu consists of two CDs, the first of which is a digest of his post-Led Zeppelin work, the second a collection of pre-Zep recordings that illustrate precisely where he and his contemporaries were coming from. The sleeve notes, which he wrote himself, are patently the work of a fanatic.

So, I ask, what was the fascination with this alien roots music, which most of those who have followed him are somewhat disconnected from? He conjures the world of the movie Pleasantville, where everything is in black-and-white until you learn to believe in yourself, at which point colour appears.

“Well, that was what music was to me. When I heard Chuck Berry singing, relating to a youth culture that sounded so gregarious and switched on, it was like a calling, like someone blowing the horn on the top of the mountain. The thing about our generation was that we had to eke out the stimulants. There was no conveyor that brought any of this to us: you could smell it, taste it, but it was the devil of a job to find it. So, when you found what you liked, it wasn’t a casual affair, it was intense. We became amazingly obsessive fans of this music.”

Why the blues, though? “It was the sound of the voice. The thing about the blues was that it sounded like tired, evil, deprived Elvis. And we all loved Elvis.”

The delightful irony is that Plant and his peers took that music further from its roots than anyone could have imagined possible. Watching Led Zeppelin’s film The Song Remains the Same, the striking thing is how little fun being a rock star in the 1970s looked in comparison with the 1960s. I wonder whether Plant envies the Rolling Stones for having stuck at it? “Oh, Christ, no — absolutely not,” he almost shrieks. “I give you my word. In every respect. Sometimes, it’s better to take a cheaper ticket and have more fun. But I was only 19 when I joined Led Zeppelin, and I didn’t know that then.”

He goes on to tell some colourful stories about touring with his old band before confessing that he would rather see Calexico than the Stones, then waxing about working with the desert-rock maverick Howe Gelb, of Giant Sand. The dinosaur days are definitely gone. Which brings us to something else that I have wondered: what is it like to be a former rock god? Does one mourn its passing? For two hours, I have been trying to ask what it’s like to no longer walk into a room and watch every woman swoon — in fact, I have been asking, but he doesn’t seem to have heard me. Finally, he does.

“No, no, I loathed all that,” he claims, “because you have to pretend that you don’t see it. I mean, people say I should no longer appear in videos with girls in their twenties and that sort of thing. In fact, that happened recently, which was ridiculous, because I happened to be dating her as well.” Which pretty much answers my question, I think.

“But you know, in other ways, your horizons expand. Before I left to see you, I was with the bloke who runs the farm next door, up in the mountains, and we were just talking about clouds. You feel more comfortable, and we have a cordiality that we would never have dreamt of when we were wired out of our brains on Peruvian flake.”

He laughs heartily, and with all this talk of clouds, we are soon onto the subject of the lyrics to Stairway to Heaven — but that will have to wait for another time.

Sixty Six to Timbuktu is released on Mercury on November 3