Customers are being duped into buying farmed sea bass and sea bream that is sold as wild by British retailers, according to a damning official report.

The Times understands that tests conducted on behalf of the Food Standards Agency have shown that fish supposed to have been caught at sea were instead reared intensively on farms.

The disclosure will heighten concerns that more affluent consumers — who spend up to £2 billion a year buying wild, free-range or organic products — are being targeted by organised fraudsters.

It follows similar concerns in other food markets where free-range eggs have been produced by battery hens, and “corn-fed chicken” were found to be dyed yellow.

The report, to be released in the next fortnight, will increase calls for further regulation of Britain’s £1 billion fish market. Consumers can pay double the price for wild fish — for the expected health benefits and a supposedly better flavour.

A source close to the report said: “There appears to be evidence, backed by authoratitive scientific tests, that there is fraudulent selling and labelling in these particular markets.

“The problem that we appear to have is that demand for fashionable fish such as sea bass and sea bream is outstripping supply, and criminals are moving in to fill that gap.”

The Food Standards Agency, an independent government department set up to protect public health and consumer interests, ordered the study.

Wild fish eat a less-processed diet than farmed fish, which alters the balance of the chemical variants, known as isotopes, of which they consist. Scientists from Eurofin, a French laboratory, collected samples of sea bass, sea bream and salmon that they could prove were wild or farmed. They then built up a database of their isotopic properties.

As a result, they could examine a fish and assess whether it had been caught at sea or reared on a fish farm.

Samples of wild sea bass and sea bream destined for British consumers had the stable isotopes of farmed fish. Wild salmon that was being sold or packaged in Italy and Norway was also found to have come from fish farms. The Times has not established whether this was destined for British consumers.

More than 4,000 tonnes of sea bass and 1,700 tonnes of sea bream were consumed in Britain in 2006, according to the Sea Fish Industry Authority. These figures are up between 15 and 20 per cent on last year because of the increasing availability of both fish in supermarkets. Celebrity chefs’ use of bream and bass has also driven up demand.

Sales of wild fish have soared after claims that farmed fish were exposed to artificial processes to increase their growth rate to a marketable size.

Environmentally-aware shoppers have also turned away from farmed fish after allegations that parasitic sea-lice have escaped from farms and destroyed native fish populations.

The European sea bass, Dicentrarchus labrax, also known as Morone labrax, is a primarily ocean-going fish that sometimes enters brackish and fresh water.

Its habitats include estuaries, lagoons, coastal waters and rivers and it is found in European waters including the eastern Atlantic Ocean, the Mediterranean Sea and the Black Sea.

Bream is a general term for a number of species of fresh-water and marine fish drawn from the Abramis family. The term sea bream is sometimes used for porgies (Sparidae) or pomfrets (Bramidae).

The FSA is also investigating a range of other fraudulent activities. There is particular concern about the authenticity of beef being sold under premium labels, such as Aberdeen Angus or Scotch beef, when it is imported meat from South America or poor-quality beef from Britain.

The growth in popularity of expensive corn-fed chickens has also caught the attention of enforcement officers. It is an easy label to put on a bird that has not eaten a crumb of corn. A new isotope test can show whether a bird has had a corn diet.

A spokesman for the FSA declined to comment on the report last week but added that the results would name and shame offending retailers. “We will release our report at some point over the next two weeks,” he said. “The tests are an important development in the fight to protect the consumer.”

Food scams

Eggs The Times reported last month how 500 million eggs may have been sold as free-range or organic when they were in fact laid by battery hens in mainland Europe

Meat In December Julie’s restaurant in West London paid more than £11,500 in fines and legal costs for serving standard meat and chicken as organic

Chicken An investigation by the FSA in 2001 found that some chicken breasts contained 43 per cent added water

Rice In 2003 the FSA tested 360 bags from shops across Britain labelled “basmati”, finding that nearly half contained 60 per cent cheaper grains

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