Former deputy prime minister Lord Prescott has accused rich countries such as the United States and Canada of trying to scupper a new climate deal.
The Labour peer said efforts to secure a successor to the 1997 Kyoto agreement, which he helped negotiate, were in danger of failing due to a "conspiracy against the poor".
He called for the clock to be stopped on the Kyoto provisions, which are due to expire next year, and a "reassessment" in 2015.
Otherwise discussions over a new deal would "wither on the vine", Lord Prescott warned.
"That is what Canada and America want, and one or two other countries," he told BBC Radio 4's Today programme. "It is a conspiracy against the poor. It is appalling.
"I am ashamed of such countries not recognising their responsibilities."
The Kyoto protocol bound developed countries to overall cuts of about 5% in global emissions by 2012, compared with 1990 levels.
But the treaty controversially spared rapidly growing economies such as China, India and Brazil from curbing their emissions.
Several leading nations - including Japan, Russia and Canada - have pulled out of the current negotiations and the US has indicated it will not join in.
UN-backed talks are taking place in Durban this week and next, but a resolution this year is considered unlikely.