The G8 leaders have struck a deal on climate change that will draw America back into the diplomatic fold on environmental issues after its refusal to ratify Kyoto.

No communiqué will be issued on the ground-breaking agreement until tomorrow, because of Tony Blair's absence from the summit this afternoon, but the deal was effectively confirmed by the President Jacques Chirac at his summit press conference tonight.

M Chirac said the terrorist bombs that forced Mr Blair to leave the Gleneagles Hotel to visit London had strengthened the resolve of the G8 leaders to reach agreement, but he denied that this was why the deal was struck. He said that the hard work had been done by the delegation "sherpas" - the officials who hold hard-fought discussions before the leaders arrive.

"This is something we have been working on with tremendous determination for days and days," said M Chirac.

"Our sherpas have spent countless hours trying to reach this agreement, and we definitely had the sense that over the last few days the US was beginning to join up to the idea of a possible agreement."

He added that America had felt the pressure of being isolated from the other seven G8 countries on the issue of climate change, and that this had helped to persuade them to shift their position enough to make an agreement possible.

A move to include five developing countries in future plans to tackle climate change had helped to change President Bush's mind, he indicated. Earlier, officials from the British delegation were diplomatically insisting that the deal had not yet been done.

"No deal has been finalised yet and the talks are still going on," a delegation official told Times Online at 5pm. Meanwhile Jack Straw, the Foreign Secretary, flew in to the Gleneagles Hotel in Perthshire to chair the afternoon session of the G8 summit after Mr Blair returned to the stricken capital. The Prime Minister made a statement before he left, pledging that the work of the G8 would not be derailed by the terrorists.

He condemned the "barbaric" series of bombings. Visibly trembling with emotion, he said: "It is the will of all the leaders of the G8 that the meeting should continue in my absence, that we will discuss the issues that we were going to discuss and reach the conclusions that we were going to reach."

A joint statement by all the G8 leaders and the visiting leaders of China, India, Brazil, Mexico and South Africa echoed this pledge that their discussions would not be affected by terror. "We will continue our deliberations in the interests of a better world," said the statement, read aloud by Mr Blair before his Chinook helicopter departed for London at 1.25pm.

"Here, at this summit, the world's leaders are striving to combat world poverty and save and improve human life. The perpetrators of today's attacks are intent on destroying human life. The terrorists will not succeed."

The blasts occurred an hour before Mr Blair was due to chair the morning's crucial meeting of G8 leaders to agree a way forward on tackling climate change that would include America. The US had been outside negotiations because of President Bush's refusal to sign up to the Kyoto agreement on limiting greenhouse gas emissions.

M Chirac revealed that after news of the bombs came through, Mr Blair was full of consternation. He quickly consulted with the other G8 leaders and agreed that another member of the British team would take over in chairing the discussions while he was briefed on the bombings.

The Foreign Secretary tonight chaired the second G8 working session between 5pm and 6pm, on the theme of foreign affairs. Mr Blair was due to return to Gleneagles later tonight to host a working dinner with fellow world leaders, and officials hope that after the extraordinary disruption of today, the remaining business of the G8 will continue as normal tomorrow.

The other G8 leaders put on a display of solidarity with the Prime Minister when he made his statement. President Bush stood on Mr Blair's right and President Jacques Chirac was to his left, putting aside bitter disagreements of recent weeks over EU reform.

Afterwards, Mr Bush gave his own personal statement on the steps of Gleneagles Hotel. He said: "The contrast is incredibly vivid to me, where we have got people here working to rid the world of poverty, stop the pandemic of Aids and working for a cleaner environment, and on the other hand you have got people killing people.

"The contrast couldn't be clearer between those of us who care deeply about human rights and liberty, and those with such evil in their hearts that they take the lives of innocent folk. "The War on Terror goes on. We will not yield to the terrorists. We will fight them and bring them to justice and at the same time spread an ideology of hope and compassion, that will overcome their ideology of hate."

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