Karol Rzepkowski is being so assailed by demands on his time that a breathless excitement has crept into his voice. “It’s a bit crazy right now,” he chuckles, “but I’m not complaining.”

He has just returned from the hatcheries at the fish farm he manages on Shetland and there is little to gripe about. For Rzepkowski, a Scot of Polish descent who once ran a Caribbean diving school, has managed to create a utopian ideal: the first completely sustainable and commercially viable method of organically farming cod.

Britons eat 300,000 tons of cod a year and it was the ingredient of choice in traditional fish and chip shops until overfishing led to dwindling stocks in the North Sea and strict catch quotas were imposed.

These days, Atlantic cod still heads the Marine Conservation Society’s (MSC) list of fish to avoid and ethically aware shoppers have stopped buying it altogether.

Yet Johnson Seafarms, where Rzepkowski is the managing director, claims to have developed a way to farm cod that is both environmentally sensitive and economically feasible. And successful too.

Their cod is already on the menu at the renowned French Laundry restaurant in California’s Napa Valley, it has been served at Hollywood events attended by Demi Moore and Pierce Brosnan, and American consumers eagerly pay top dollar for it to be imported.

Last week, organic cod fillets went on sale for the first time across the UK in Tesco stores, and Sainsbury’s will stock the range — called No Catch . . . Just Cod — later this month, at a price on a par with wild fish. “It’s about £6 a pack, which is approximately the same as you pay for a good piece of Aberdeen Angus beef,” says Rzepkowski. “We’re saying to customers: ‘Here you go, we’re trying to do it right, we’re trying to meet all the modern ideals, but it’s never going to be for nothing.’ We piloted the product in America to see how it would work. We’ve had a lot of success. If it didn’t taste right, people wouldn’t buy it, no matter how environmentally friendly it is.”

Fish farming is an industry tainted by its past. The mass production of salmon, which involved the use of chemicals and poor farming practices, still casts a long, dark shadow, and not everybody is convinced by this conversion in ethos in cod farming.

Bruce Sandison, the chairman of the Salmon Farm Protest Group, says: “Seventy-five per cent of the stock of a Norwegian cod farm was lost to a new disease called Francisella. Has a complete and independent risk assessment been carried out? All the same assurances were made with salmon farming and this lurch into cod will result in the same mistakes.”

Sandison is convinced that cod farming, even if it claims to be sustainable and organic, will follow the same route as the salmon industry when the cold reality of the business world begins to take hold. “It’s a very interesting use of the word ‘organic’,” he adds. “When most people hear organic, they think it means natural, but there’s nothing natural about large-scale cod farming. There are terrible risks involved. The same errors will be made again.”

Johnson Seafarms is adamant, though, that it has learnt lessons from the salmon industry’s detrimental impact on the environment and consumer confidence.

The company switched to cod three years ago because it is better suited to being farmed — the fish shoal naturally and graze slowly.

The firm, based in the village of Vidlin, insists on only using first-generation farmed fish — their parents are wild cod from the surrounding coastal waters — so if any were to escape they would not impact on the local population.

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