They provided the stunning setting for a Bond and a Jaws film, and the 1960s Flipper TV series about a super-intelligent bottlenose dolphin. But today the beaches and azure waters of Clifton Bay in the Bahamas are at the centre of a real-life drama that would surely compete with anything Hollywood could invent.

The sprawling development of the peninsular home of the billionaire fashion tycoon Peter Nygard and his plans to build a stem cell research centre there, not least due to the 71-year-old's interest in keeping ever youthful, are said by a campaign group to be threatening an environmental calamity on one of the world's most beautiful coastlines.

And, in a twist that introduces allegations of corruption to an already compelling plot, evidence has now emerged of a "cash-for-favours" letter penned by Nygard some 30 years ago.

The correspondence dating from 1992, unearthed by a local newspaper, was addressed to the current prime minister of the Bahamas, Perry Christie, when the politician was a junior government minister. Highlighting $42,000 worth of political donations, Nygard asks among other things for a swift official name change of the land where his home has been built so that it will be known as Nygard Cay.

That way, Nygard writes, Forbes magazine may refer to it in its upcoming "lives of the rich and famous" photo-shoot at his property. "Obviously, this whole world is based on one hand helping the other and you know that I am prepared to do whatever is in my capacity to help out the Bahamas and the PLP [Progressive Liberal party] and of course yourself in any way I can," Nygard says.

The plot may seem far-fetched, and there is no evidence that Christie, elected as prime minister of the Bahamas in 2012, responded favourably to the letter. But, campaigners say, the environmental risk to beaches is real. In 1984 Nygard bought his home on a peninsula above Clifton Bay, at the northern tip of Nassau, the island that serves as capital of the crown dependency. It is claimed that through building structures and laying down sand and concrete in the waters he has gradually increased the size of the estate from three to six acres. His activities, it is claimed, have encouraged sand to deposit and create beaches around the Nygard property. This, they say, has prevented the usual flow of sand accumulating at one of the Bahamas' most beautiful public beaches, Jaws.

"Nygard epitomises the worst kind of unregulated and cosy and incestuous relationship between government and foreign developers", said Fred Smith, a QC and co-founder of the Save the Bays campaign group. "The government and such foreign developers think that our society, culture, environment can be sacrificed on the altar of the almighty dollar.

"The change in the flow of the sand matters environmentally because erosion begins to occur, marine habitats are destroyed, and there is less and less beach. At some spots in Clifton Bay there is just honeycomb rock now where there was once a beach."

Nygard was ordered by the government of the Bahamas in 2010 to return his property and estate, formerly known as Simms Point, to its original size. But there was a change of government, and Nygard claims that the order no longer stands, adding that the sand accumulation around his plot is natural. The Canadian has instead sought permission from the new government, led by Christie, to further develop Nygard Cay.

Nygard, founder of one of the world's biggest female fashion companies (also called Nygard), has held talks with the Bahamas Investment Authority about investing $30m in building a stem cell research facility with his home patch being one possible site.

Nygard, in an interview with the Bahamas Tribune, said he believed he was "taking perhaps more stem cell treatment than anybody else in the world". He added: "Stem cells are being used for anti-ageing and the University of Miami is doing a study about that to prove that it is true. They are looking at me, and my markers have shown exactly that I have been actually reversing my aging and getting younger."

Nygard's spokesman did not respond to questions. The businessman has previously accused the Save the Bays campaign of being a tool of a neighbour, Louis Bacon, a billionaire hedge fund manager with whom he has been in a land dispute, which the campaign has denied.

The Save the Bays campaign confirmed that Bacon was a large donor but insisted that it was a coalition of concerned residents and environmentalists. When asked previously whether he had donated money to the Progressive Liberal party, Nygard has said he did not know. He told reporters: "I've been supporting people for the last 30 years. I don't measure in terms of amounts of money. I've been a people's person all my life and been supporting various causes. I have not been political".