Leaders from the Christian, Jewish and Muslim faiths have urged Tony Blair to play "the fullest part" in helping the world's poorest countries.
Tony Blair has put assistance to Africa at the top of the G8 agenda
The prime minister must use the UK's G8 presidency to help "halve extreme poverty", they say in a letter.
The G8 leaders must cancel the debt of the poorest nations, they add.
The letter is from by the Archbishops of Canterbury and Westminster, the Chief Rabbi, the Council of Mosques and Imams chair and the Free Churches head.
It marks the first time they have spoken together publicly since their joint statement calling for peace in March 2003 ahead of the Iraq War.
Archbishop of Canterbury Dr Rowan Williams told the BBC: "It is up to all of us, governments and people, to keep the pressure up and make sure that this is not just a one-off event.
"I think, in a sense, we need to be more angry about the situation than we are."
Dr Williams also said it looked like they were "pushing at an open door with our own government" after Prime Minister Tony Blair put assistance to Africa's poorest countries at the top of the agenda for the G8 summit in Gleneagles, Scotland, on 6 to 8 July.
On the question of debt relief, he said they were "optimistic".
"Trade reform is a bigger and longer issue," he said. "What we expect to see I think is a long-term commitment, not a quick and magical solution."
He also called on African countries to "rally round" and "put the kind of pressure that's needed" on Robert Mugabe's controversial regime in Zimbabwe.
Tuesday's letter said: "The UK's chairing of the G8, along with its presidency of the EU, require and challenge Britain to play the fullest part now in seeking to change the structures and practices that result in suffering and privation.
"We hope and pray that the opportunity will be grasped with urgency."
The security and wellbeing of all nations "depends on the security and wellbeing of each nation", it adds.
"A world divided by poverty cannot be healed without justice."
All the leaders at the summit must use their "huge power" to meet the international community's goals of halving extreme poverty and hunger in the next decade and reducing infant mortality by two-thirds.
"We must treat these as solid commitments and not as flags in the wind," the religious leaders said.
Their vision, shared by other faiths around the world, was not being lived up to, they wrote.
The fact that 30,000 people died avoidable deaths every day proved this, they added.
They welcomed "steps in the right direction" towards cancelling the debt of the poorest nations.
But achieving "the vision" also meant "changing the terms of international trade to allow developing countries to make the most of their trading potential", they wrote.
"It means using our own wealth and prosperity to the benefit of all; it means promoting good governance for every citizen.
"It means not impoverishing and depleting the planet God has entrusted to our stewardship."