"Tonight, Bono is Joe Strummer". In a studio in New York recently, for the amusement of himself and those assembled, the U2 frontman growled out a corrosive Stars In Their Eyes-style take on a new song featuring lyrics by himself and the former leader of The Clash.

Originally, '48864' – Nelson Mandela's prison number – was set to be recorded and filmed by Bono and Strummer for the forthcoming televised AIDS-benefit concert, 'Mandela SOS' on Robben Island in South Africa. But now, in the aftermath of the sudden death of the 50-year-old Strummer, Bono will have to go it alone for real.

'48864' had Strummer providing the verse and Bono the chorus to go over "a hi-life music bed that Dave Stewart and some African musicians are doing," the U2 singer explains, the day after he has attended The Gangs Of New York premiere in Dublin. "Joe sent me in some lyrics and they were great, really honest, just like The Clash at their finest. That's how I ended up doing a version of it in New York as Joe Strummer. He's a town crier of a voice; I couldn't speak after it, but I had a laugh."

But there's no laughing about it now.

"He was actually supposed to be coming to Dublin this very week," Bono reveals. "I suppose I'm going to have to finish it myself now, I'm going to have to be Joe for keeps. And it's a shame because I was really looking forward to singing it with him."

Bono now expects that his version of the song will feature on an upcoming AIDS-benefit album for which the U2 singer has already cut tracks with Dr Dre and Dave Stewart.

It was at a seminal punk concert in Dublin nearly 26 years ago, that The Clash, with Joe Strummer centre stage, made their mark on the teenagers who would go on to become U2.

"The Junior Common Room, Trinity, 1977," Bono recalls, the images still vivid. "We were 16/17, and we went to this. They opened up their backdrop just before they came onstage and the image was of riots from the back of the first album cover. And there was a real sense of threat and danger in the crowd. I mean, at that stage, there was only about 200 people who were into punk rock in Dublin and a lot of them were poshies spitting at each other. But in the middle of it there was still a real sense of threat as well as a strong sexuality coming off the stage, from Paul Simenon and the way they dressed.

"It was a real luminous moment for me – Xerox is probably more apt, it just really imprinted itself on me. It was the moment when I realised that music could spill over a stage and into the real world and into your life and carry you away on its tide. That really was a major event for our band."

Unlike some who are inclined to misty-eyed reverence when it comes to retrospectively championing the "authenticity" of The Clash, Bono wasn't always overly impressed by some of the poses struck by the self-styled last gang in town.

"I thought there was plenty fake about The Clash," he laughs. "I knew there was a certain amount of posturing, and at first that offended me. And then I realised that that didn't matter. And I knew that, musically, Strummer came from a pure rock 'n' roll background – The 101ers – and I knew that the politics were something he was feeling his way through. Then there were stories sneaking out that he had quite a middle-class background, and they were trying to cover that up [laughs].

"But in amongst all the show business of The Clash – of The Clash, not Joe Strummer – there was a true soul, trying to figure it out, trying to explain himself to the world, and trying to explain the world to us, who knew very little about it. I mean, I certainly wouldn't have visited Central America; back then I didn't know who the Sandinistas were. So much of my agit-prop education came via people like The Clash. Or John Lennon. Or Bob Marley."

Then there was the sheer thrill and pleasure of encountering that rare thing: a white rock band with a real understanding of the rhythms of Jamaica.

"Reggae, yeah," Bono agrees, "and dub and ska and bluebeat, and that whole intoxicating other world that was out there in terms of hearing about Chile or Cuba or places like Brixton. There were all these things coming off The Clash. And later Mick Jones and B.A.D. played with us many, many times. And I can't tell you how much we respected Mick Jones' musicality and his actual, just, decency. They all, as it turned out, had a real decency – that old-fashioned word.

"In fact, it was all kind of old school in a weird way. I mean, Joe had a ’50s thing going on. And I think that was something to do with the fact that the ’50s was still a very idealistic time; the world could be coloured and bent into any shape you wanted. Joe held onto that, ’cos that was when there was most promise in the west."

Did Bono run into Joe much over the years?

"We played together in the US Festival and I met him a few times apart from that. He was always very good about our band and I thought that took a lot of grace, considering we, in a lot of ways, filled in the space that they left. Especially in America. Even though we, as a band, have been interested in lots of different things, it was a door The Clash walked through that, before it shut, we jammed our foot in. And when they left the scene we kind of had it to ourselves. And no other band from this side of the Atlantic has passed through that door since. Not one. Which is interesting."

Asked how he'll best remember Joe Stummer, Bono says: "As a great lyricist and a kind of offhand educator and town crier. [Barks]: Know your rights!"

And, finally, a favourite Clash song to remember him by?

"'Straight To Hell'," says Bono. "Which is one place he's not going."