Three hours after the "Danish text" had been leaked to the Guardian, Lumumba Di-Aping, the Sudanese chairman of the group of 132 developing countries known as G77 plus China, spelt out exactly why the poor countries he represents were so incensed. "The text robs developing countries of their just and equitable and fair share of the atmospheric space. It tries to treat rich and poor countries as equal," said the diplomat.

The text is a draft proposal for the final political agreement that should be signed by national leaders including Barack Obama and Gordon Brown at the end of the Copenhagen summit on 18 December. It was prepared in secret by a group of individuals known as "the circle of commitment" but understood to include the US and Denmark.

Five hours later, the UN's top climate diplomat had responded. Yvo de Boer said: "This was an informal paper ahead of the conference given to a number of people for the purposes of consultations. The only formal texts in the UN process are the ones tabled by the chairs of this Copenhagen conference at the behest of the parties [involved]."

But the representatives of developing nations felt betrayed by the intent of the proposals in the draft.

"This text destroys both the UN convention on climate change and the Kyoto protocol. This is aimed at producing a new treaty, a new legal initiative that throws away the basis of [differing] obligations between the poorest and most wealthy nations in the world," said Di-Aping.

The existing treaty is the only global agreement that legally obliges rich countries to reduce their emissions.

Di-Aping is one of the most outspoken of developing country leaders, at once charming and radical.

What the west had failed to grasp, he said, was the very deep hurt that had been growing steadily since the climate negotiations were effectively taken over by heads of state and were conducted outside the UN, the only forum in which poor countries feel they are equally represented.

The text is now likely to be withdrawn because of its reception by China, India and many other developing countries. It suggests that rich countries are desperate for world leaders to have a text to work from when they arrive next week.

Few numbers are included in the text, because these would be filled in later after negotiation by world leaders.

However, it does seek to hold global temperature rises to 2C, the safe limit according to scientists, and it mentions the sum of $10bn a year in aid to help poor countries cope with climate change, starting in 2012.

Last night the G77 reaction was seen by some developed world analysts as an exaggerated but fundamentally correct response to the way that the US, the UK and other rich countries have sought to negotiate.

Development NGOs were particularly scathing in their criticism.

Antonio Hill, climate policy adviser for Oxfam International, said: "This is only a draft, but it highlights the risk that when the big countries come together, the small ones get hurt."

Hill added: "It proposes a green fund to be run by a board, but the big risk is that it will run by the World Bank and the Global Environment Facility [a partnership of 10 agencies including the World Bank and the UN Environment Programme] and not the UN.

"That would be a step backwards, and it tries to put constraints on [emissions in] developing countries when none were negotiated in earlier UN climate talks."

A spokesman for Cafod, a development charity with close links to some of the poorest countries in the world, said: "This draft document reveals the backstage machinations of a biased host who, instead of acting as nonpartisan broker, is taking sides with the developed countries.

"The document should not even exist. There is a UN legal process which is the official negotiating text. The Danish text disrespects the solid, steady approach of the UN process."

Over the next days several new texts will emerge and out of them a likely contender to be carried by consensus of all the countries. Di-Aping said that the G77 remained committed to the talks.

"We will not walk out of the talks at this late hour, because we will not allow the failure of Copenhagen. But we will not sign an inequitable deal; we will not accept a deal that condemns 80% of the world population to further suffering and injustice."

Later this week, the rich countries can expect fresh assaults from the Africa group of countries, the least developed countries group, and the association of small island states. Each is liable to upset the best laid plans of developed world leaders who those groups say appear to place the need to reach an agreement above fully engaging with the poorest countries.

"We call ordinary people to put the utmost pressure on politicians to come to their senses," said Di-Aping.