Britain and its partners at the Copenhagen climate summit were accused of 21st century "carbon colonialism" today over a draft agreement that developing nations say would discriminate against them.

The so-called "Danish text" was leaked yesterday and prompted an angry reaction from the G77 bloc of developing nations, which warned that its members would not sign an "inequitable" deal when the conference ends with a summit of world leaders next Friday.

The G77's chair, Lumumba Stanislaus Di Aping of Sudan, went on the attack again today, telling journalists that the Danish text "seemed to secure 60 per cent of the global atmospheric space for 20 per cent of the world's wealthiest nations".

Mr Di Aping was especially critical of the Danish Prime Minister, Lars Lokke Rasmussen, whom he accused of being desperate to achieve a deal at any price.

He issued an appeal to Barack Obama, who is scheduled to arrive in Copenhagen next Friday, not to join in any attempt to strong-arm developing nations into signing a deal that would leave their countries exposed to the ravages of global warming.

"We humbly ask of President Obama that the new dawn of multilaterialism that he promised should not be simply business as usual – the West prevailing at the expense of the rest of the developing countries," Mr Di Aping added.

European delegates pointed out that the text in question was dated November 27 and had never been formally tabled. "It's a storm in a teacup," one said.

Others said that the G77 was simply trying to head off any deal that would oblige developing nations to commit to carbon emission limits. Under the Kyoto Protocol, they are exempt from any such obligations.

The text also came in for criticism on the floor of the conference, where a Singaporean activist, Amira Karim, won loud applause after attacking it for overturning and subverting normal UN principles. "This imposition without discussion is tantamount to carbon colonialism," she declared.

But even within the G77 the divisions were clear.

The Pacific island of Tuvalu, one of the most vulnerable to possible rising sea levels, fought unsuccessfully to have its own draft text, submitted in June, formally adopted on to the agenda. The resolution would entail massive aid to help vulnerable nations.

The proposal was backed by a string of island nations and by delegations from sub-Saharan Africa but rejected by China and India, the most poweful member of the G77, which blocked a proposal to set up a formal working group.

The key battles being fought out in the negotiations include a decision on whether the Kyoto Protocol should be allowed to lapse when the current obligations it imposes expire in 2012. Developing nations want to stick with it while Western nations including the United States – the world's biggest emitter per capita of greenhouse gases, but which never ratified the Kyoto agreement – want an entirely new agreeement.

The UN's chief climate diplomat, Yvo De Boer, said that he expected "two tracks" to emerge from the Copenhagen meeting: a continuation of the Kyoto Protocol and a new agreement bringing in the United States and setting emission limits on developing nations.

Another sticking point is who would hold the purse strings if, as expected, industrialised nations agree to pour tens of billions into "quick-start financing" to help mitigate the effects of climate change.

The United Nations estimates that the fight against climate change may cost about $300 billion (£184 billion) a year in the long term, and the Danish text appeared to hand over responsibility to the World Bank. Developing nations have called for a global climate fund.

A possible compromise could emerge later today when four nations – Britain, Australia, Mexico and Norway – propose a new green fund that would handle the finances in any accord.

A British official said a document to be published later would look at ideas for the fund, which would help developing nations to adapt to climate changes.

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