Protectionism costs the global economy $500 billion a year, according to research released by the government.

Publishing a new study on international trade, Gordon Brown and Patricia Hewitt stepped up their calls for a renewed effort to deliver free trade.

And they warned that the European Commission should go further than its current proposals to end common agricultural policy export subsidies.

The EU should agree to "significant further agricultural reform" including the reduction of all agricultural tariff peaks towards the maximum level for non-agricultural products.

The Common Agricultural Policy (CAP) costs taxpayers within Europe €50 billion per year, plus a further €50 billion in artificially high food prices.

"Whilst locking developing countries out of the international trading system, the CAP also fails to deliver on its core objectives, as EU farm incomes continue their steady relative decline and Europe's poorest households face higher food prices," said a government statement.

The chancellor and the trade secretary also said they would urge other world leaders to recognise the benefits of free trade.

Poverty

Ministers are linking their push for trade liberalisation with wider moves to tackle third world poverty.

"We cannot proclaim ourselves supporters of development while preventing developing countries from selling us the products they can produce most efficiently," said Brown.

"Protection is highest in agriculture and labour intensive goods - precisely those areas in which developing countries are most competitive.

"Reducing barriers to trade in agriculture could benefit developing countries by $240 billion a year - more than three times as much as current annual aid flows."

Brown also said he would be warning other G7 countries in talks this weekend that continued protectionism also puts global economic growth at risk.

But the call for the first world to overhaul its trade practices was coupled with a reminder of poorer nations that they also need to reform trade practices as part of their own development policies.

Hewitt said the experience of Europe showed that "countries that trade together also grow together".