Scotland's £1 billion salmon farming industry is facing growing difficulties winning public support for massive expansion plans after a concerned local community was labelled a "vipers' nest" in a leaked company email.

Emails from within the foreign-owned Scottish Salmon Company, which produces one-fifth of Scotland's farmed salmon, also reveal its public relations tactics for avoiding the "angst, time, delay [and] hoo-haa" caused by objections.

The company planned to locate small salmon cages on a loch and "let the locals get used to it" before applying to introduce larger ones in two or three years' time. The aim was to avoid "lengthy, tiring, negative PR battles".

The revelations have sparked fury amongst fish farm opponents, who accuse the company of betraying "cynical contempt" for local people by hiding their plans for future expansion. However, the company alleges that campaigners have distorted the facts in an attempt to discredit the fish farming industry.

Farmed salmon is Scotland's largest single food export, and one of the country's most important rural industries. Production has risen nearly fivefold over the last decade, and now involves 30 companies at about 250 sites along the west coast and on the islands. But its expansion has come at a cost, with local communities and environmentalists increasingly alarmed about pollution, the damage to coastal scenery and threats to wild fish.

Now the industry, backed by the Scottish Government, wants to further boost production of all farmed fish 50% by 2020. This is resulting in escalating conflicts, as proposals for new and bigger salmon farms emerge.

One of the fiercest flashpoints has been at Plocropol, on the east coast of Harris in the Outer Hebrides, where the Scottish Salmon Company wanted to expand a fish farm. But the plan ran into strong opposition from local fishermen.

On March 2 last year, the company's environmental manager, Rebecca Dean, emailed her chief executive, Stewart McLelland, to discuss tactics.

She wrote: "Plocropol is a guaranteed vipers' nest with the huge delays that will create, and the demands on council (and the Scottish Salmon Company) time could be better spent on other sites that may be less oppositional." The problems "couldn't get much worse than Ploc", she added.

She suggested "filling the council's time" with proposals for fish farms elsewhere on the Western Isles. Existing salmon cages at Plocropol could be left for the local community to "get used to" in the hope that they would accept bigger cages in the future, she argued.

In reply, McLelland wrote: "I agree with your thinking." He proposed expansion elsewhere and then possibly giving up the Plocropol site "on our terms", adding: "This way we ensure we get the good publicity and demonstrate the advantages of working together."

The email exchange was leaked to anti-fish-farm campaigners and posted on the "FishyLeaks" website last week. According to one local group, Outer Hebrides Against Fish Farms, it showed that the Scottish Salmon Company's public consultations were "just a cynical PR stunt designed to fool local people".

And it alleged: "The company clearly has a hidden agenda for expansion by the back door."

The campaign group's spokesman, Peter Urpeth, argued that the leaked emails cast doubt on the Scottish Salmon Company's public statements. "Local communities trust this company as stewards of the local environment: that trust is now clearly misplaced," he said.

The environmental campaigner that runs the FishyLeaks website, Don Staniford, said the emails revealed the "utter contempt foreign-owned salmon farming companies have for local communities in the Western Isles".

In a statement in response, the Scottish Salmon Company – which is backed by investors from Norway and Switzerland and is registered in the tax haven of Jersey– alleged that the release of the emails was part of a concerted campaign to discredit the company and the industry.

McLelland said: "It is unfortunate that the wording of out-of-date internal communications is being used by a few individuals to distort the facts. Once again, rather than contribute constructively, they wish to create confusion and offence where none was intended."

He insisted: "Local communities who work with us know us and should be assured that we have the utmost respect for them."

The planned expansion at Plocropol was withdrawn following public consultations.

The war of words on Harris is being replicated nationally, in submissions to an inquiry into fish farming by the Scottish Parliament's rural affairs, climate change and environment committee. The industry has accused campaigners of badgering government agencies with freedom of information requests with the aim of eroding public confidence in farmed salmon.

Chief executive of the Scottish Salmon Producers' Organisation, Scott Landsburgh, said: "Misinformation from campaigners is designed to undermine the Government, its regulators and the overall economic benefits of salmon farming."

But this was dismissed as "nonsense" by Guy Linley-Adams, a solicitor for the Salmon & Trout Association in Scotland, which represents anglers. The aim of most campaigns, he argued, was to "strengthen the hand of regulatory authorities in their control and oversight of environmental impacts".

Leaked emails 'betray cynical contempt for local feelings'