Radiohead, one of the UK's most popular and political rock bands, have turned down a request to play at Live 8.
Radiohead singer Thom Yorke is a vocal campaigner on global issues
Singer Thom Yorke has campaigned on some of the same global issues as Live 8, such as the reform of trade laws.
But a band spokesman said they could not play because the band were too "spread out" and guitarist Jonny Greenwood's wife had just given birth.
Yorke and Greenwood did appear on the Band Aid 20 single. The Live 8 concerts take place in five cities on 2 July.
The London leg of the event in Hyde Park will feature Madonna, U2, REM, Coldplay, Robbie Williams, Sir Elton John and Sir Paul McCartney.
Fans have until midnight on Sunday to enter a text message competition to win one of 72,500 pairs of tickets.
Fans have until Sunday to text to win tickets for the London concert
Radiohead spokesman Murray Chalmers said: "They were asked but they can't do it.
"Jonny is out of action because he and his wife have just had a baby and the rest of the band are spread out all over the place at that time."
The spokesman added he did not know whether the band endorsed Live 8 and its aims.
In April, Yorke joined an all-night protest in Westminster Abbey to call for "trade justice" for the world's poorest workers.
He said he was seeking an end to "a series of misguided economic policies".
Live 8 is aiming to raise awareness and pressure to improve the plight of the poor in Africa ahead of the G8 summit near Edinburgh.
Organisers are demanding reformed trade laws to give African traders a fairer deal, a cancellation of international debt and increased aid.