The campaign from Project Slingshot features Chris Packham criticising the Scottish farmed salmon industry, with a video titled ‘Gaslit’ published on YouTube having amassed over 85,000 views after six days.

Adverts were placed at train stations in London, depicting discoloured salmon being eaten by lice. One advert showed Packham with text overlay, which read: ‘They say their farmed salmon is “planet-friendly”. I don’t buy it.’

Project Slingshot named businesses such as Scottish Sea Farms, Cooke Aquaculture, Bakkafrost and Mowi in its campaign, claiming that they were polluting waters and using “toxic chemicals”. It also stated that 100% of Scottish salmon sold in UK supermarkets is factory farmed.

The campaign website signposted ways for consumers to contact Scottish Government to stop funding the salmon farming industry, and urged visitors to the website to email M&S and tell the retailer to stop selling factory-farmed salmon.

Responding to the campaign, Scottish Sea Farms stated: “We are a proud salmon supplier and 50% of our Scottish salmon is sold to UK consumers through multiple retailers including Tesco, Co-op, Waitrose and M&S. Salmon is an affordable, nutrient-rich protein which is a staple of our diets and we are committed to farming responsibly with the highest standards in the industry for fish health and welfare, with the lowest stocking densities.

“The salmon industry provides circa 11,000 jobs in the UK, and every single farmer at Scottish Sea Farms looks after the health and welfare of salmon on their farm to the absolute highest standards.

“To meet the demand for one of the UK’s most popular fish, we need to farm salmon, and we do that responsibly in conditions that replicate their natural environment as closely as possible. That means deep, cold sea lochs and seas with fast-flowing, well-oxygenated waters and strong currents.”

“If campaigners drove Scottish salmon off supermarket shelves, demand would not disappear – it would simply be met by more imports.”

A Salmon Scotland spokesperson said: “This is not an independent assessment of Scottish salmon farming. It is the latest campaign from a vegan-led activist group that has already targeted the pig and chicken sectors and is backed by substantial US funding.

“Its co-founder has commercial interests in plant-based alternatives, including businesses that have faced financial difficulties.

“The claims present a distorted picture and come amid growing concerns about overseas ‘dark money’ funding campaigns against the sector. These activists do not speak for the thousands of people whose livelihoods depend on Scottish salmon, or the millions of consumers who choose the UK’s most popular fish.

“If campaigners drove Scottish salmon off supermarket shelves, demand would not disappear – it would simply be met by more imports, often from countries with lower standards and a bigger carbon footprint.”

In response to Project Slingshot, M&S told journalists the campaign was “misleading”, stating: “Salmon is a nutrient-rich, healthy protein. It is an excellent source of the omega-3 fatty acids that are required in our diets. Without farming, this important protein would be unavailable to millions of families across the UK. M&S salmon is farmed responsibly to the highest welfare standards, supporting an industry that offers thousands of UK jobs.

“M&S farms uphold the highest standards of welfare – exceptionally low stock density with just 1.5% fish to 98.5% water, continuous water quality monitoring, high-quality feed and vet care. We only work with select farms that we know and trust and they are independently monitored and we are proud that Scottish Sea Farms has been our supplier for over 20 years.”

The retailer said it was not true that wild or farmed salmon was grey, noting that a nutrient called carteniods in their diet helped to keep them “healthy”, giving their flesh a pink colour. It said in farmed salmon the nutrient was added to their feed to replicate a wild diet.

M&S also stated that chemicals were not used on salmon meat, with supplier Scottish Sea Farms using veterinary medicines prescribed to fish “only by exception if needed by vets”. It noted that these were “robustly controlled” by the Scottish Environment Protection Agency.