“Something's wrong with a food system in which cod caught off Scotland is transported to China and then back to be eaten.”

The globe-trotting trek made by cod has been condemned as “madness” and “ridiculous” by Scottish fish producers, fishermen and environmentalists. And it happens despite pledges by supermarkets and food producers to reduce their climate pollution and food miles. The revelation also raises questions about the environmental and social impact of the globalisation of the Scottish food industry. “Surely it would make more sense to process the fish here,” said Hugh Raven, director of Soil Association Scotland , which backs organic food.

The fish is caught in the North Atlantic, deep frozen, shipped to China for processing by workers earning less than £1-a-day before being refrozen and returned to Scotland.

Cod caught off Scotland is being sent on a 10,000-mile round trip to China and back again to be filleted for supermarkets, shops and chip suppers.

Raven pointed out that Scotland also exported beef, salmon and grain at the same time as importing large amounts of the same goods. “If we want to make our food production more sustainable, we must get better at feeding ourselves,” he argued.

Scottish prawns and langoustines are also being hand-shelled in China and Thailand while Atlantic haddock caught off Scotland is being prepared in Poland. Blended whisky is exported as far away as Australia to be bottled.

The Scottish Fishermen’s Federation (SFF) has confirmed that cod landed by Scottish and other European Union fishing boats are transported to China. Although the fish are landed fresh they have to be put into cold storage for the journey.

"It is frozen for transportation, then unfrozen for processing, and refrozen for the return journey and then unfrozen again for sale on the shelves," said the SFF’s chief executive, Bertie Armstrong.

“The joke that ‘a fish travels more dead than alive’ is no longer a joke but has become reality.”

Armstrong pointed out that, although the North Atlantic was the source of the natural resource, it was the international market which dictated where and how it was produced and sold.

“The fishermen have no control over what happens. That is in the hands of the processor,” he told the Sunday Herald.

“It was a great surprise to me that it is commercially viable to process Scottish cod in China. At the very least it is ironic and at worst idiotic when food miles are taken into consideration. But it is simply market driven.”

Because of its cheap labour, China has become the world’s biggest processor of fish and it is now a major supplier of cod fillets to Europe. The cod is shipped via the Suez Canal.

Friends of the Earth Scotland condemned cod’s Chinese journey. “This shunting of goods back and forth across the globe in environmental terms is absolute madness,” said a spokesperson for the environmental group.

”It’s a real shame to think that this food could have been eaten fresh in Scotland, but is instead shipped around the world to make a processed, packaged product.”

Other food mile offenders include Dawnfresh, a seafood company in Uddingston that supplies supermarkets and other large retailers. It cut 70 jobs in 2006 after deciding to ship Scottish prawns more than 5000 miles to China to be shelled by hand.

The prawns are then shipped back to the River Clyde in Scotland and breaded for sale as scampi in Britain. The company said it was forced to make the move by commercial pressures.

Another company, Young’s Seafood, was criticised in 2006 for sending langoustines to Thailand to be hand-shelled while closing a mechanical shelling plant in Annan, Dumfries and Galloway, with the loss of 120 jobs. It argued, however, that the change caused less pollution.

Britain’s biggest supermarket chain, Tesco, has also sent its Atlantic haddock for processing to Poland where labour costs are lower. Even green-minded Prince Charles’s organic company, Duchy Selections, has chosen Alaskan salmon - which is shipped thousands of miles - to be smoked in Scotland.