The major multiples have brushed aside scare stories about farmed salmon published in the Daily Mail and other newspapers.

And they expressed their confidence in renewed Food Standards Agency advice to eat one portion of oily fish a week, as well as in the quality of Scottish product.

Lobbyists Don Staniford and Bruce Sandison propagated a US study, published in Science magazine, which alleged people should only eat farmed salmon three times a year due to cancer risks from contaminant levels.

A Tesco spokesman said: “The coverage was quite alarming but we are mirroring the FSA’s advice and this will continue.

“Salmon sales are strong and there has been no great move away from this as a result of this sort of newspaper story, so the good advice is getting through.”

Both Asda and Sainsbury reported strong sales growth for salmon last week, on a record of consistently strong sales.

An Asda spokesman said sales were up 20% last week. “Read the papers and you would think there are shelves of farmed salmon going to waste. This could not be further from the truth. The sales figures speak for themselves.”

Morrisons said it was encouraging shoppers to “enjoy salmon” and reported no impact on sales from adverse publicity, recently or in the past.

Sainsbury said its product, whether from Northern Scotland or Norway, was fully traceable to farms that comply with comprehensive welfare, environmental and safety requirements. “All of the results in the Science article are within EU safety limits,” a spokeswoman added.

Salmon from European fish farms have "much lower" levels of toxins than those set by international agencies, said Norway’s National Institute of Nutrition and Seafood Research, rejecting the Science study.

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