'We are gathering for you the largest ever mandate for action'

We are gathering for you the largest mandate for action in history. Just as people demanded an end to slavery, demanded women's suffrage, demanded the end of apartheid - we now call for an end to the obscenity of extreme poverty that is killing 50,000 people every day, in the 21st century.

"Shall we say obscenity or absurdity?" asks the singer.

"Absurd is better," replies Curtis. It's less over the top, he discreetly refrains from saying.

In the next room Comic Relief director Kevin Cahill is lounging on a brown leather sofa with people organising not today's concert but the one in Murrayfield in Scotland on Wednesday, on the eve of the G8 leaders meeting in Gleneagles. "We're getting there," he says, "after a week of running orders, effing and blinding, people dropping in and dropping out, and the sound of egos clashing." The problem now is will there be a message from the Dalai Lhama or not?

Geldof's cellphone interrupts, as it constantly does. No conversation with him lasts more than a minute without the punctuation of his mobile. He has it constantly on speakerphone, so all conversations are public.

"We've got a problem with Oleg Volker."

"Who?"

"He's the guy in charge of Russia's cosmonaut programme. He says they can't fit it in, getting someone from space to introduce one of the songs."

"Tell him we need it. We want to hear Jonathon Ross saying: 'And now over to space'."

"We've told him that."

"Find out who his boss is and get him on the line for me. And get me the Russian ambassador."

The next section of the open letter is ready. On Aid:

Deliver an extra $25bn aid for Africa and make plans to ensure this aid really will be effective at eradicating poverty. This must stand beside a further $25bn for the other poorest countries of the world. This is the absolute minimum required to begin to win the battle against extreme poverty.

The doorbell rings. Into the room is ushered Birhan Woldu. She is the girl whose face was seen in the Live Aid concert, a hand gently stroking her forehead above her sunken eyes and parched lips. The nun caring for her said she only 15 minutes to live. The footage was the most poignant moment of the event which stopped the world that day 20 years ago. She is the living proof that Live Aid worked.

Today she is a 24-year-old agriculture student, petite, smiling, her hair in tight plaits, dressed in a crisp, white shirt and new denims. Geldof calls out her name. She hugs him, tightly. When she pulls away he asks: "You finished your exams?"

Curtis looks on from the sofa as Geldof conducts his conversation through an interpreter. Curtis says nothing, but as his fellow campaigner's jaunty conversation continues with the young Ethiopian, Curtis's bespectacled eyes begin slowly to fill with tears. After all the talk about 30,000 children dying needlessly in Africa every day he is overwhelmed with the enormity of a single life saved.

"Would you like to speak at the concert?" Geldof asks the girl.

"In front of 200,000 people?" says Curtis, finding his voice.

"It's important she speaks if she can. People become real when they speak. We can write a couple of sentences for her if she wants."

"Something about hope for the future," suggests Curtis.

"No, none of your activist bollocks," says Geldof. "She's just an ordinary girl whose nervous about whether she's passed her exam or not."

Birhanlives in a tiny village in the Ethiopian highlands and this is only her second trip away from it. She has not heard of Paul McCartney or U2 or Elton John. But she has heard of Madonna.

"OK," says Geldof. "We'll do it just before Madonna's set. I'll introduce you. You can say a few words. But you must wait for the applause to die down between each sentence. Don't talk over the noise of the crowd." Birhan nods. "Then Madonna will come and take you by the hand and lead you off stage and then she'll come back on."

Geldof's phone rings. "I have to get there earlier than that. I have to start the Gay Pride march. Why? Because they had Hyde Park booked before us and they gave it up for us. So it's to say thank you."

Birhan waves goodbye. She's off to buy some trainers. Geldof waves. The phone rings again.

"Absolutely no chance of any tickets. There were only 1,000 VIP ones and they've all gone. The corporate ones they had to pay for. How do you think we're paying for this fucking gig?"

His conversation is drowned by a shriek from one of Curtis's female staff at a desk submerged in post-it notes. She has just taken a message. "Brad Pitt's in town. And he's coming here."

"Here," shrieks a colleague.

"He's coming for a meeting with Bob."

"Here!"

Scream.

The next part of the open letter has been agreed. On Debt:

Confirm the 100 per cent debt cancellation from the G8 finance ministers meeting and commit to 100 per cent debt cancellation for ALL the countries that need it and remove damaging economic policies that are imposed as a condition.

"Have we heard from that O'legless guy in Russia yet?"

"Do you think the punters will understand this bit about the IMF imposing unhelpful policies on African countries?" asks Curtis.

"The punters mightn't understand that," says Geldof, "but the G8 leaders will. This is for two audiences."

There is a call from Paul Wolfowitz, the architect of the war in Iraq, whom George Bush has made president of the World Bank. Geldof talks to him for 20 minutes. At the end he says: "So what would be great would be if President Bush could come to Gleneagles with a dynamic package that wouldn't cost the US much. A bit more money for girls' education ... perhaps another $1.5bn, which would get us up to the $25bn a year we need. And a proposal to fix a date to end export subsidies. Thanks for ringing. See you in Scotland. Bye."

As Geldof puts down the phone there is a cry from the next room. "Lindsay Davenport's in the women's final! Great! The game will be so boring that everyone will switch over from Wimbledon to watch us."

Geldof doesn't hear. He's back on the phone. "Just say yes to them and then do what you want. Tell them you got their letter and then just follow your own agenda." He flicks through The Sun as he listens. "They say U2 are only doing one song. Where do they get this bollocks?"

The next bit of the letter is ready. On Trade:

Make decisive steps to end the unjust rules of trade, and allow poor countries to build their own economies, at their own pace. It is only through trade that Africa will eventually beat poverty on its own.

"Brad! Hi man."

Curtis's staff shriek. Geldof grins: "Fooled you!"

There's another call. Tony Blair has organised a delegation to meet the G8 leaders on Wednesday night. "Who else shall we have apart from Bob and Bono?" asks Curtis. "Would the Archbishop of Canterbury come?"

"They're rich. We're poor. We promised. We didn't deliver. I remember going to Galway as a child and seeing kids in the streets in bare feet. I remember that Ireland.

"Now we've got a decent life. But when you do that you have to remember. You have a duty to give back. Hold on I've got America on the other line. I'll get back to you."

Technically, the Russians can't do the space link-up. Nasa say they won't for political reasons. "Well, go to the White House chief of staff," says Geldof. "And tell them not to be so silly."

"Ok dude, keep going, we've just got 24 hours to go."

We will not applaud half-measures, or politics as usual. This must be a historic breakthrough. Today there will be noise and music and joy, the joy of exuberant possibility. On Friday there will be a great silence as the world awaits your verdict. Do not disappoint us. Do not create a generation of cynics. Do not betray the desires of billions and the hopes of the poorest of our world. Are those 50,000 people each day to be allowed to live, or not?

The man in charge of the Hyde Park site is on the line, an assistant says. "He says no car parking on the site."

"Tell him to change that," says Geldof. "I'm not going to fucking walk home like I did last time."