Tony Blair today said the G8 needed to back him in a "quantum leap" in aid and trade to relieve poverty in Africa, as he shared a stage with Bono and Bill Gates at the World Economic Forum in Davos.

Switching his attention from climate change, the subject of his opening address last night, to Africa, the prime minister said that if the disease and death that ravaged that continent happened anywhere else in the world, it would be seen as a major scandal, rather than ignored.

And he announced that Britain would be contributing a further £45m towards provision of mosquito nets - seen by the World Health Organisation as one of the most important ways of reducing malaria.

Nelson Mandela, who is also attending the summit of global business leaders, said he would be backing the Make Poverty History campaign at a visit to London next month, where he will address a rally in Trafalgar Square.

Mr Blair, before leaving Switzerland and handing the UK delegation's leadership back to chancellor Gordon Brown, told a press conference that he would be pushing for action when his Commission for Africa reports back in March.

He said: "A few years ago I described Africa as a scar on the conscience of the world.

"The facts as we see them and as they are happening in the daily lives of the people in Africa are so shocking it almost defies our imagination.

"If what is happening in Africa today was happening in any other part of the world, there would be such a scandal, such a clamour, governments would be falling over themselves to do something about this."

He said that the African Commission which he established with African leaders would be bringing forward new measures later in the year.

Oxfam director, Barbara Stocking, who is at Davos, welcomed the PM's commitment on Africa, but urged him to use next week's meeting of the G7 to cancel all debt.

"Next week in London, at the G7 Finance ministers meeting, rich countries will have their first chance of 2005 to turn the rhetoric on ending poverty into action. Cancelling all of the bilateral and multilateral debts of the world's poorest countries would free up huge sums of money to be spent on education and health and would only cost people in rich countries the equivalent of a cup of coffee a year till 2015," she said.

Mr Mandela will be in London for a G8 summit next month, where, at midday on February 3, he will speak to an expected crowd of thousands at a rally in Trafalgar Square in a bid to encourage public participation in the anti-poverty blitz.

The move is also designed to pressurise world leaders into fulfilling their pledges to increase and improve aid for the poor, deliver trade justice and provide further debt relief, the organisation says.

Adrian Lovett of Oxfam, a member of the Make Poverty History coalition, said: "Nelson Mandela's presence in London sends a clear signal from one of the world's greatest heroes that 2005 is the year when we strike a huge blow against world poverty.

"His presence is not only a rallying cry to the public to get involved, but serves notice to rich countries that the world will not put up with false promises, delays and hollow soundbites.

"This has to be the year that rich countries take action and increase their aid budgets, reform the rules of trade and finally end the debt burden that is destroying the livelihoods of millions of people."

Make Poverty History is a coalition of charities, faith groups, campaigns, trade unions, and celebrities, garnering backing from stars including Coldplay singer Chris Martin, Bono, Claudia Schiffer, Scarlett Johansson, Jamelia, Fran Healey from Travis, the Sugababes, Graham Norton and Stephen Fry.

Bono - who appeared at last year's Labour party conference - said at Davos that Britain's presidency of the G8 offered an "historic opportunity". He said that his role was to persuade politicians to take the difficult decisions necessary to achieve that.

"I suppose my job as a rock star and activist is to bring applause when people get it right and make their lives a misery when they don't," he said.

"I think I have some use here to try to encourage people to take some unpopular decisions at home and do the right thing on the global stage.

"These are expensive choices people have to make if they want to do the right thing for Africa."

The three men appeared later on a platform alongside former US president Bill Clinton, South African leader Thabo Mbeki and Nigerian president Olusegun Obesanjo to discuss the problems facing Africa.

President Obesanjo welcomed Mr Blair's Africa Commission initiative but said the continent needed more direct aid. "We are not getting the critical mass of funds to make development possible," he said.

Mr Clinton acknowledged that there was little public pressure in America for the US government to act but said he believed that was changing.

"Nobody will ever get beat for congress or president for not doing it," he said. "We have never created an effective political constituency but it is coming."

He said that the American public had raised a "staggering" amount for the victims of the Asian tsunami and he now wanted to see that impulse transformed into regular assistance for the developing world.