New data has found that salmon sold in many British supermarkets is laced with up to 20 times the acceptable rate of sea lice.

The Salmon and Trout Conservation Scotland compiled the information as part of a survey regarding salmon in the UK's food industry.

The group found that on average, three lice were discovered in every fish that was farmed, three times the maximum level expected.

The findings also found that the sea lice numbers were "out of control" and farms were routinely failing to meet required industry standards.

Andrew Graham-Stewart, director of S&TC Scotland, said: "Sea lice numbers on farmed fish across much of the industry are of epidemic proportions.

"More worrying, the Scottish Government's flagship new policy appears to be a sham, little more than a cynical 'widening of the goalposts' to the industry's advantage, a policy with no teeth."

The group said that they would be writing to supermarkets, urging them to stop the sale of salmon from the worst farms.

The group took particular aim at the Scottish government over the way it revealed the numbers regarding lice in salmon.

Guy Linley-Adams, solicitor for S&TC Scotland, said: "It is now abundantly clear why Scottish ministers tried so hard to prevent the publication of individual salmon farm figures and thus shield the Scottish salmon farming industry from proper public scrutiny."

One of the worst affected was Co-op's salmon supplier, with 6 out of its 10 farms exceeding acceptable lice levels.

Sainsbury's supplier Marine Harvest and Tesco supplier Grieg Seafood Shetland were also on the list. Grieg was found to have salmon with an average of 22 lice.

However, despite the high levels of lice in the fish, they pose no risk to humans as they are either destroyed or treated with pesticides before being sent to supermarkets.

The Scottish government has been approached for comment.