International climate negotiations have made slow progress partly because developing nations are suspicious that the rich world is using the issue as "an excuse" to keep them poor and maintain the global status quo, according to the former UN climate chief.

Yvo de Boer, speaking before crucial climate negotiations in Cancún, Mexico, next week, said the suspicion among poorer nations was an important roadblock to a deal at the UN climate talks in Copenhagen last year.

The Dutchman, who left the UN earlier this year after four years brokering UN climate agreements, said that many countries were not deeply committed to a green growth economic model that climate change demanded.

"Although many nations play lip service to this model, most of them, deep in their hearts, are unsure. In fact, many developing nations fear that the intent of the west is to use climate as an excuse to keep [them] poor and maintain the current status quo," he said.

His comments came on the same day that the UK's energy and climate secretary, Chris Huhne, played down the prospects of a legally binding agreement at the talks, which open on Monday.

"We are not expecting a final agreement. The objective is to reinvigorate the talks. Success means getting the world to within shouting distance of a deal, keeping the show on the road and making practical progress on areas like forestry, finance and reduction commitments," Huhne said.

De Boer today also warned politicians heading to the next round of international climate talks not to be too ambitious. "The lesson for Cancún [is] keep it simple, keep it practical, and don't overreach," he said.

He admitted this approach would be "selling the climate short", but urged realism over idealism. "My approach would not be enough to limit temperatures to a maximum 2C rise," he said. "[But] a modest start can be an effective way to get the ball going. We need to work with what we have in the same way that President Nasheed of the Maldives accepted the Copenhagen accord at last year's Copenhagen summit – not because he liked it, but because he realised it was the best he could get," he said in an opinion piece in the science journal Nature.

Huhne, who will be in Cancún for the second week of the talks, said countries should try to "anchor" the commitment on action made by 80 countries following last year's talks at Copenhagen.

The UK is keen for Europe to move to the more ambitious end of its range of commitments made last year – an EU-wide cut in emissions of 30% on 1990 levels – which it believes is in the bloc's economic interests.

But he said that the EU was prepared to accept a second phase of the Kyoto protocol if a parallel, legally binding treaty to cover countries including the US and China is achieved.