Britain's top aid charities have told the Prime Minister that genetically modified foods will not solve world hunger, but may actually increase poverty and malnutrition.
Their intervention – in a joint submission to the Government's official debate on GM crops and foods – strikes a devastating blow at a central plank of its support for the controversial technology.
Tony Blair and key advisers have wholeheartedly supported the claims of the biotech industry that GM crops are needed to feed the world. Two years ago a Cabinet report claimed they could win the war against hunger, and the year before the Government's then hugely-influential scientific adviser, Lord May, said it was his main reason for supporting them.
But Prince Charles provoked private Prime Ministerial fury by describing this argument as "suspiciously like emotional blackmail".
The new submission – signed by the directors of Oxfam, Christian Aid, Save the Children, Cafod and Action Aid, and sent to Mr Blair's Strategic Unit in the Cabinet Office – puts the moral and practical authority of leading anti-hunger crusaders behind the prince and against the Prime Minister.
The charity leaders say claims that GM crops will feed the world are "misleading and fail to address the complexities of poverty reduction". They acknowledge that the technology may have "potential benefits" but are concerned they will not help the small farmers and poor people in the rural Third World where their groups have practical experience.
They call on the Prime Minister to take a "precautionary approach" to the technology, rather than giving it his enthusiastic support.
The charities say GM crops are likely to create more poverty. They point out that hunger is not caused by a shortage of food, but because the poor cannot afford to buy it.
In the past, new agricultural technologies like the Green Revolution have tended to be taken up by rich farmers. They increase production and force poor farmers out of business.
The charities fear that introducing GM technology will have even more catastrophic effects because it is dominated by a few multinational companies. Salil Sheehy, the director of Action Aid, says: "Farmers will be caught in a vicious circle, increasingly dependent on a small number of giant multinationals."
But in a remarkable initiative, the World Bank last week brought together Oxfam and Greenpeace with the biotech giants Monsanto and Syngenta to try to reach an agreement on the technologies needed to feed the world.
The meeting in Dublin – which also included ministers and officials from 19 governments and representatives of eight UN agencies – decided to start a series of consultations which could lead to the most comprehensive international assessment of the risks and benefits of biotechnology, organic farming and other new agricultural techniques.