More than 40 music stars recorded a new version of Band Aid single Do They Know It's Christmas? in London, culminating in a group session on Sunday.
By Ian Youngs
BBC News entertainment reporter at Air Studios
The recording studio was packed with some of the UK's most popular artists and was a celebration of Britain's musical talent.
Busted were converted to the Band Aid cause
But it was not a day of glamour, egos or schmoozing, and they were told in no uncertain terms the day was not about them. Bob Geldof made sure of that.
If any stars had a tenuous grip on reality, Geldof brought them down to earth with a jolt, leaving most - from Joss Stone to The Darkness frontman Justin Hawkins - in tears.
Just before they got together for the group photo, Geldof decided to play them a 20-year-old video of the Ethiopian famine.
It was the most moving video from Live Aid, showing dying refugees in 1984, and has lost none of its power.
Stone, the 17-year-old soul sensation, was aghast throughout, mouth gaping and hand helplessly held against her face.
Other superstars who are used to the world revolving around them were also in the huddle, equally rapt and upset.
Will Young recorded two lines with Jamelia
Geldof, who knows how to tug the heartstrings, then introduced a woman from the wings who was seen as a starving child at the end of the video.
It was too much for some artists and there will be many red eyes in the group photo that followed.
It was a wake-up call to some young singers that their influence and responsibilities stretch beyond the record shops.
And 20 years after the original, it was an overdue reminder to the rest that there is still a world outside their windows.
At the start of the day, Stone - who was not born when the original song came out - mistakenly called Geldof "Gandalf" and James Bourne from Busted did not recognise the man who started it all.
But by the end, the young stars were won over and Busted were saying they wanted to show the Band Aid logo and video on tour.
"Cool or uncool - what does that mean on a Sunday morning when you haven't shaved and your make-up is still dripping from the night before?" Geldof asked.
"If you can sing like a voice from God, who cares, cool or uncool? Spare me. Rock or pop - so? All that goes and it just becomes a bunch of people on a Sunday morning noodling about the place."
Geldof has a certain way of getting his message across, making stars an offer they cannot refuse.
He basically tells them if they do not take part, and help raise money for famine relief, they are directly responsible for the deaths of other people.
His achievement in getting such a stellar line-up together 20 years ago was more impressive because this time, most of the current stars were eager to take part.
But today's singers did not escape his legendary persuasion.
Keisha Buchanan of Sugababes said she knew a bit about Band Aid before this weekend - but did not know how "deep" it was.
"Today, when we saw that video, that's when it hit home about how serious it is," she said.
Bandmate Heidi Range added: "It just brings home what it is all about because everyone can get a bit excited and carried away recording the song. But after seeing that, everyone was really upset."
The Darkness singer Justin Hawkins said he and guitarist brother Dan both cried.
"But then Frankie [Poullain, bassist] goes 'You pansies, you've let the band down. You're men'."
It was a day of mixed emotions and contradictions.
It did not take long during the group photo and following chorus for the mood to lighten - but the original song always had an uplifting element, as well as the darker message, to appeal to the pop kids.
With more stars than the average Brit Awards, the day also had a distinctly unreal edge.
From Blur's Damon Albarn in a pink apron handing out tea - but not singing - to Heidi from Sugababes trying to play drums, the artists were clearly not too precious about their images.
As more than 40 arrived for the photo and chorus at lunchtime, it was impossible to not walk around the building without bumping into a platinum-selling star.
And at times, there was a queue of big names waiting to come into the small press room, which contained four radio reporters, one press and one online journalist.
Squeezing past Busted, Keane, Sugababes and The Darkness is something a few million pop fans would probably sell their grandmothers to do.
Among the artists, there were inevitable friendships between those who already knew each other or shared a style, but all knew they were in it together and were happy to do their bit.
There were as many big stars as 1984, but the number of TV crews, radio reporters, security men and PR people was a sign of the times.
"It's like watching a Spielberg movie unfold," according to Midge Ure, who produced the original single and was co-producer this time. "It's huge, it's brilliant."
Ure and Geldof want people to buy 50 copies of the single and give them their money again - but there is another, less quantifiable and longer-term objective this time.
"This year, when people buy your record," Geldof told the singers, "they're making a political demand. Next year, we must keep this pressure up."
And the music? The rough version and chorus sounded suitably great. But of course, that did not really matter.