By Helen Dunne

It may have been the film he always dreamed of producing but The Passion of Christ was also the film that three years ago allowed Hollywood actor Mel Gibson to fulfil his fantasy and buy a private island. Gibson spent $15m on Mago (pronounced Mango), a 5,500-acre tropical island in the remote Northern Lau group of islands in Fiji, nestling in the Pacific, complete with powder white beaches, turquoise lagoons and flowing spring water.

He joins a growing list of Hollywood stars, multi-millionaires and businessmen who can claim to be ruler of their very own island. Nicholas Cage, Diana Ross, Tony Curtis and Brooke Shields have all succumbed to temptation, while Marlon Brando arguably started the fashion when he acquired Tetiaroa in French Polynesia shortly after filming Mutiny on the Bounty in 1965.

Others, however, have been granted asylum. Icelandic pop singer Bjork was given the local isle of Ellidaey by the country’s prime minister as a reward for having ‘enhanced the glory and fame of Iceland’. “It is like having your own kingdom,” explains Cheyenne Morrison, owner of Coldwall Banker Morrison’s Private Islands, which has more than 180 islands on its books. “Even if the island is small, owning one is the pinnacle in one-upmanship.”

It also provides a solution to today’s thorniest question, how to get away from it all. “Isolation has ceased to be a form of deprivation,” adds Morrison. “Isolation is the scarcest commodity.” Unsurprisingly, sales of private islands have also escalated since 9/11. “It’s the fear of terrorism, coupled with the fear that the quality of life is disappearing,” explains Farhan Vladi, owner of German-based Vladi Private Islands, who has sold more than 1,800 islands in his career. “The two anxieties are linked.”

But isolation also brings its own problems. Agents recommend that buyers should only consider islands that are within a 90-minute helicopter or boat ride from a doctor. Similarly, many available islands are completely untouched. Ronde, a 2,000-acre island off the coast of Grenada, is currently on the market for $70m. It is a diver’s delight, with underwater visibility exceeding 30 metres and a swim-through cave that opens to an underground cavern decorated with stalactites and quartz crystals. It has no amenities, such as food supplies, running water and accommodation, and would require huge sums of money (and some ingenuity) to make it habitable.

Alexis Pappos, director of operations at Private Islands Inc, explains: “Developing an island with utilities will cost 50% more than comparable mainland development. But new technology, such as solar and wind power, and reverse-osmosis water filtration are making island development far more cost-effective.” Morrison adds: “When one succumbs to emotion, one often does not act in a logical or analytical fashion. Conduct a proper and professional due diligence of the island, exactly as you would for any other kind of real estate.”

The checklist for island buying includes a good water supply, freedom from pest and adequate and viable landing sites (salt water will cause jetties to rot). A deep-water route and good anchorage are essential because supply boats need to deliver groceries and furniture.

And there are also maintenance costs to consider. Plumbers, for example, will need to be flown in if the sewage system explodes. “Islands require quite a bit of work to maintain,” concedes Pappos. “Transportation can be an issue during inclement weather, so it is very advisable that one chooses a property that will be accessible by boat or aircraft during the months that it will be used. As islands may be quite isolated, security can pose a problem. Many clients employ caretakers or staff for this reason.”

While the high profile islands change hands at eye-watering price tags, some smaller islands are available for less than the cost of a central London apartment. Vladi claims the average price of the islands he has sold is $300,000.

It seems he is not exaggerating. Bull Gut Island, a 19-acre Atlantic ocean escape on Mitchell Bay in Nova Scotia, is currently available for $400,000 (£200,000), while Lower Turtle Rock, a 1.4 acre island off the coast of Great Abaco near Treasure Cay in the Bahamas is priced at $200,000 (£100,000). Closer to home, Shore Island on the River Shannon in County Clare, Ireland, has an asking price of €900,000 (£600,000).

Owning an island can prove a tremendous investment. Long before Sir Richard Branson became rich and famous, he dreamed of owning a private retreat. He found Necker, a 74-acre island in the British Virgin Islands, which was on sale for £3m. He offered £150,000 and, in a stunning property market coup, acquired it three months later for £180,000.

Sir Richard has spent $13m developing the island, which today is valued at more than $130m. It is also available for hire from $46,000 per night for up to 28 guests.

"Even if the island is small, owning one is the pinnacle in one-upmanship." Cheyenne Morrison, Coldwall Banker Morrison’s Private Islands

Apart from the problems of development, there is the thorny issue of dealing with the governments in the region. For example, the Virgin Islands’ government decreed that Sir Richard had five years to develop Necker or lose his ownership rights.

It is currently not legal for foreigners to own land in the Philippines, which requires potential buyers to form consortiums with local partners, who will own 60%, while only a fraction of the land in Fiji is available to non-citizens. The islands in the Maldives are all owned and sold by the government on lease agreements, although islands in the Americas and Caribbean are generally available on freehold.

And in the Bahamas, it can take many months to close a deal after some members of the Medellin drug cartel turned one Bahamian island into a logistics hub. All potential owners are now checked out and must disclose intentions for their islands to the government.

The only consistent advice to any would-be purchaser is to rent an island before signing on the dotted line. “You can’t test a marriage for three months, but you can try living on an island,” points out Vladi.