Bono, lead singer with the Irish rock band U2, has urged Labour to "get real" and deal with the problems of world poverty and the Aids crisis.
The conference delegates will form a smaller than usual crowd for Bono
Tony Blair and Gordon Brown were the John Lennon and Paul McCartney of the global development stage, he said praising their achievements.
But he urged the pair to "finish what they started" and end world poverty.
Britain had a real chance to effect change when it took up the G8 presidency next year, he said.
If a rich country "with the reins of power in its hands" could not lead the fight against world poverty then critics who called him "Labour's apologist" would be right, he said.
The star and global campaigner called for action to combat the spread of Aids and ease Africa's debt burden.
He praised the government's decision to increase its contribution to the global fight against HIV/Aids but said there was more to do.
"I'm fond of Tony Blair and Gordon Brown. They are kind of the John and Paul of the global development stage, in my opinion.
"But the point is, Lennon and McCartney changed my interior world - Blair and Brown can change the real world."
"It's not about charity it's about justice," he said reminding delegates of the thousands dying in Africa for the lack of medicines available in high street chemists in the UK.
'Continent in flames'
He told delegates the fight against world poverty was a cause as noble as when their grandparents fought the Nazis.
He went on: "Africa makes a fool of our idea of justice; it makes a farce of our idea of equality. It mocks our pieties, it doubts our concern, it questions
"Because there's no way we can look at Africa - a continent bursting into flames - and if we're honest conclude that it would ever be allowed to happen
"Anywhere else. Certainly not here. In Europe. Or America. Or Australia, or Canada.
"There's just no chance."
He continued: "You see, deep down, if we really accepted that Africans were equal to us, we would all do more to put the fire out.
"We've got watering cans; when what we really need are the fire brigades."
His speech focused on the work of his Debt, Aids, Trade Africa (Data) organisation as well as his backing for a campaign called Make Poverty History.
Bono is the latest in a string of high-profile speakers from around the world to address the annual gathering in recent years, following on from Nelson Mandela, Bill Clinton and Afghanistan president Hamid Karzai.
The singer has been a long-time campaigner on the need to fight the spectre of Aids in Africa and recently spoke at both the Republican and Democrat party conventions in the US.
He has also been instrumental in the Drop The Debt campaign, which wiped out millions of pounds of international debt owed by Third World governments.
His campaigning work - which he fits in alongside a busy rock career that sees his band release their 14th album in November - has led to calls from several quarters for him to be considered for a Nobel Prize for humanitarianism.