Supermarket giant Sainsbury's has been accused of selling "responsibly sourced" Hebridean salmon from a loch hundreds of miles away.

Sainsbury's Taste The Difference salmon is packaged with the claim that it is "reared in sheltered, fast-flowing seawater locations around the Isles of Skye, Lewis and Uist".

But the Salmon and Trout Association (S&TA) claims that it is actually sourced from Loch Fyne, a sea loch more than 200 miles from Skye, in Argyll that they allege is polluted with unacceptable levels of sea-lice, chemicals, faeces and diseases.

Sainsbury's website also says that its supplier of salmon is Marine Harvest but the farms listed are owned and operated by a competitor, The Scottish Salmon Company, according to the association.

S&TA has reported Sainsbury's to the Advertising Standards Authority and Trading Standards.

Sainsbury's has admitted that there has been "an error" in its packaging due to a recent change in supplier and apologised to customers.

The association's complaint states: "Sea-lice numbers on farmed fish in excess of industry thresholds, benthic pollution with sea-lice treatment chemicals in excess of environmental quality standards, escapes of farmed fish, unsatisfactory organic pollution of the seabed with uneaten food and faeces and farmed salmonid diseases have all been recorded in Loch Fyne."

Guy Linley-Adams, solicitor to the S&TA aquaculture campaign, said: "Quite apart from issues of identifying exactly where its farmed salmon comes from, the S&TA believes Sainsbury's must substantiate its 'responsible sourcing' assertions with hard facts about named farms, and not just general assurances.

"Without this, discerning consumers may not have confidence in what they are being asked to buy."

Hughie Campbell Adamson, chairman of S&TA Scotland, said: "Supermarkets have a duty to be honest and transparent about the food they sell.

"Farmed salmon, grown in open-net marine cages, can come at a heavy environmental cost, not least in its impact on wild salmon and sea trout.

"We believe that Sainsbury's should now require all the farms from which it sources its farmed salmon to publish weekly farm-specific sea-lice parasite counts against which claims made by the fish farmers can be properly assessed."

A Sainsbury's spokeswoman said its "responsibly sourced" salmon is reared on RSPCA Freedom Food approved farms on the West Coast and Islands which participate in approved schemes which monitor standards and good agricultural practice.

She said: "We are very proud of our record on responsible sourcing of fish; Sainsbury's is the country's largest retailer of RSPCA Freedom Food Salmon and all our Scottish Salmon is farmed to a number of independent standards.

"Unfortunately, there has been an error in the information on the packaging of some of our Taste the Difference salmon products in recent months.

"We are now resolving this and sincerely apologise to customers, who can be reassured that there has been no impact on our industry-leading sourcing standards."