"Universal trade liberalisation may offer fresh markets and promise overall in-creases in wealth," he said. "It also forces choices on vulnerable countries, whose effects may be - in the short to medium term - very costly indeed to a generation of workers, to the environment, to political stability."

Dr Williams chastised wealthy countries for failing to practise what they preached. "The rich protect their markets while talking about the virtues of free trade," he said, in a reference to the US steel tariffs raised in 2002 and European Union agricultural subsidies.

Christian Aid and other campaigners, including Cafod, Actionaid and Oxfam, have formed the Trade Justice Movement with a mission to promote fair, rather than free, trade. Christian Aid said yesterday it was not opposed to the principle of free trade but to forced trade liberalisation.

Dr Williams criticised the practice, pursued by the World Bank and other donors, of making aid conditional on free market reforms, such as privatisation and trade liberalisation.

"Global agencies have often held up sustainable economic growth in poor countries by insisting that it can only be allowed to develop in the way they dictate. Debt repayment has constantly distorted the possibilities of stability, let alone growth," he said.

There is a growing belief among some donors and development experts that attempting to force aid recipients to carry out policies against their will is counter-productive. Commenting on the archbishop's words, Hilary Benn, international development secretary, said: "Developing countries should be able to carry out trade reform in their own way and at their own pace - no country should be forced to liberalise."

Eamonn Butler, director of the Adam Smith Institute - which takes its name from the man regarded as the founder of free market economics - did not welcome "rock stars and archbishops pretending to be economists". But Dr Williams was right to say wealthy nations often employed protectionist measures. It was these that were to blame for starvation in developing countries rather than free trade. "In the long run, free trade creates the greatest possible benefit for everyone."

Stephen Redding, of the London School of Economics and a member of the Centre for Economic Policy Research, said: "Most professional economists believe the policies of protection and import substitution have failed in the developing world."

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