Gordon Brown's preparations for the G20 summit suffered a third blow in as many days last night with the latest jolt coming from the minister responsible for organising the global get-together.

Lord Malloch-Brown, the Foreign Office minister, declared that "incumbency is hell nowadays", noting how every government was "struggling with terrible opinion polls and very angry people".

After the bland promises of the G20 summit in Washington last November, he insisted: "We can't again engage in meaningless, empty commitments which don't survive the flight home."

Yet the peer also indicated that people should not get their hopes up about what next Thursday's London summit could achieve, saying: "The global economy is going to go on descending on April 3. The massive destruction of wealth that is going on is not going to be stopped by any leaders' communique."

He added: "Stock markets may be arrested and turned around but we are in for a very tough 2009 under any circumstances."

Following the warning from Mervyn King, the Governor of the Bank of England, against another spending splurge in the forthcoming Budget, and after Mirek Topolanek, the Czech premier, branded America's fiscal stimulus "the road to hell", the Tories pounced on Lord Malloch-Brown's remarks.

Eric Pickles, the Conservative chairman, said: "With Gordon Brown out of the country, another of his ministers has dared to tell the truth about the failings of the Prime Minister's leadership and his stewardship of the economy. This government and its economic policies are falling apart by the minute."

In Brazil, the PM's call for a $100bn (£69bn) package to revive international trade was in danger of being upstaged after his host launched an attack on the "white, blue-eyed people", who had caused the economic crisis.

President Luiz Inacio Lula Da Silva, who is white, told a joint press conference he had never met a black banker and argued that the poor should not suffer as a result of mistakes by the rich. "This is a crisis that was caused by people, white with blue eyes. And before the crisis they looked as if they knew everything about economics."

"Once again the great part of the poor in the world that were still not yet (getting) their share of development that was caused by globalisation, they were the first ones to suffer."

The UK Government sees Brazil as a key ally in getting agreement at the G20 summit. Its economy had been growing quickly until exports slumped by 25% in just three months because of the downturn.

Mr Brown warned that this year worldwide trade was projected to fall for the first time in 30 years.

"Literally thousands of businesses who want to trade around the world are being prevented from doing so by the absence of trade credit available to them. I'm going to ask the G20 next week to support a global expansion of trade finance of at least $100bn to help revive trade in all parts of the world," he said.

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