In one of the more surprising additions to the Live 8 running order, Microsoft chairman Bill Gates made a brief appearance to lend his support to the event.

Introduced by Sir Bob Geldof before a somewhat incredulous crowd, Gates urged world leaders to do more to fight poverty, and called on people to act.

"If you show people the problems and show people the solutions they will be moved to act," he said.

"The world is beginning to demand more action on poverty. We know what to do. Some day in the future all people, no matter where they are born, will be able to live a healthy life."

Gates concluded by introducing Dido, the next act on stage.

However, his 30-second speech was unlikely to have been witnessed by most viewers in the US where television coverage was limited. It was also unavailable via the Bill and Melinda Gates Foundation website.

Johnathan Ross, presenting the event for the BBC, somewhat predictably made light of Gates's surprise appearance. "Perhaps he could stick around to explain why Windows keeps crashing," he suggested.

A number of other celebrities also made fun of Gates during subsequent interviews with Ross.

Sir Bob Geldof, in contrast, praised the work of the Gates foundation and hailed Gates as the world's most important philanthropist.

Gates announced in January this year that his foundation will donate $691m towards life-saving vaccines for millions of children in poor countries.