The hammock, I am reliably informed, was invented by the Arawak indians who once inhabited the Virgin islands, and in 1783... actually it doesn't matter a fig what happened in 1783 because, when you own a private island, history, geography and just about everything else are whatever you choose to make them.

If you like Bali but have got fed up with the journey, the climate or possibly the government, you can, like Richard Branson, create your own Balinese island in the West Indies. And if you want to call one of the buildings Bali Hi and another Bali Lo, no one is going to stop you.

Branson first saw Necker in 1979 when, posing as a multi-millionaire, he was given a red carpet tour of available islands by some very upmarket estate agents who installed him at an expensive hotel and flew him around by helicopter. The asking price for Necker was £2m. He offered £175,000. The red carpet was pulled from under his feet and he had to pay his own fare home. Later, when he really was a multi-millionaire, the island was still hanging on the market, and he was able to buy it in 1981 for the comparatively knock-down price of £200,000.

Not that Necker was anything special as West Indian islands go. About three-quarters of a mile long and half a mile wide with a hill some 100ft high running down the middle, it had two good beaches but no buildings, no fresh water and very few trees. The only previous known residents had been the journalist Andrew Alexander and the photographer Don McCullin who were landed there in 1968 to write an article for the Weekend Telegraph on what it was really like to be marooned on a desert island. And a miserable time they had of it.

It is now more comfortable. The houses have been built in traditional Balinese style with no obvious expense spared. The timber and the dark stone for the walls were brought from Brazil, the honey-coloured floor stone from Yorkshire. The statues, furniture and fabrics came from Indonesia. The goats who roamed the island were "persuaded to leave".

Branson spends three months of the year on Necker, keeping open house for his friends, and he considers it his home. When he isn't there, the island is available to rent to the likes of Steven Spielberg, Harrison Ford, Robert DeNiro, Bryan Ferry, Mike Oldfield, John Hurt, Peter Gabriel, Rosanna Arquette, Oprah Winfrey, Michael J Fox, Mel Gibson, Annie Lennox and George Michael - and you if you have the odd $14,000 a day to spare on a holiday.

You arrive at Necker from Tortola at 50 miles an hour in an enormous white speedboat, the kind that the talented Mr Ripley would certainly have envied. A dozen or so staff live on the island, all young, fair-haired and bronzed. The women look like Greta Scacchi circa 1985, and - even stranger - the men are like younger, better-looking versions of Branson himself. The resident staff tend to the guests, teach tennis and sailing and drive the speedboat on sunset cruises. They seem disconcertingly like the Midwitch Cuckoos come of age, but they are more than happy to treat you, me and "Richard" as their equals. The cleaning and general maintenance is performed by a further staff of 20 who are brought in for the day from Tortola, but not in the speedboat.

The buildings are, by any standards, spectacular. The house on the hill has views of the sea on all sides, and a breeze blows through every room and corridor. Plants grow in the hall, almost a jungle in the main lounge. Most of the bathrooms are open-sided, and you can watch the ocean while standing in the shower or sitting on the lavatory. (The last time I was in a bathroom with a wall missing was in a squat in Clapham, but it wasn't the same - the view only went as far as the tumble-down house next door.) Some of the lavatories are covered in Balinese mosaic, the shower walls built from coral and driftwood.

The rest of the island is proving more intractable to Balinisation. Hundreds of trees have been planted as well as cactus and frangipani, but the strong winds, fierce sun and poor soil cause problems, and the shade is insufficient to sustain the ornamental gingers, ferns and orchids that define a Balinese landscape. Most of the colour comes from tecomas, oleander, hibiscus and too much purple bougainvillea.

The island is not yet full of sounds and sweet airs - unless you count David Gray and early Bob Dylan - and half way between the quay and the main house a strong smell wafts from what I was told is the "organic wildlife pond". When you own a private island, a malfunctioning sewage plant can become an organic wildlife pond any time you want.

When they were here, Alexander and McCullin lived on a dismal diet of what few fish they could catch, stale coconut, sea grapes and prickly pears, spending hours trying to remove the fine prickles from their mouths. Sitting at the long dining table on the veranda, I could look down to the beach where they lived, and I often thought of them as I ate quails eggs stuffed with caviar and drank Chateau Lynch-Bages (perhaps a little too young) or the Necker-branded champagne.

The food on the island is an elaborate concoction of sculpted vegetables artistically arranged, open ravioli of lobster and fennel, duck and foie gras, chargrilled snapper and tempura prawns, and strange stick-like objects tied up with seaweed which you don't know whether to eat or use as cutlery. Differently-coloured sauces are dripped elegantly around the plate like a painting by Jackson Pollock. It is all rather in the style of Raymond Blanc of whom Private Eye once said: "Surely this man would eat his own toes if the right recipe occurred to him."

In the long term, this diet is unlikely to do you any more good than Alexander and McCullin's, although if you wanted something simpler, you would certainly get it. You could even have beans on toast, but it would probably come in a perfect pyramid topped with a sprig of dill.

Alexander and McCullin slept on the beach, soaked by the rain and eaten by mosquitoes. McCullin counted 51 bites on the back of one hand, and on the first night, his last words were: "I do not much like what I see." As I lay in my large comfortable bed under the mosquito net, listening to the roar of the surf and watching the intense blue of the Caribbean night sky, the thin white curtains blowing in the breeze, I rather liked what I saw. My last thought on the first night was that a couple of Howard Hodgkins might possibly have brightened up the walls a bit.

Alexander and McCullin were desperate with thirst for most of their stay, never able to collect enough rainwater. Had they been here now, they would only have had to stroll a few yards through the bushes to find an open-sided pagoda where there would have been an ample supply of clean towels, sun-tan oil (factors nought to infinity), snorkelling gear and a fridge full of cold water, cans of beer and bottles of champagne.

They had probably intended to stay for months, but after a fortnight they gave up, each having lost about two stone. Were they staying here now, a fortnight's stay would set them back $196,000 - an awful lot of money for a holiday, but the island is booked up far in advance and many guests come back regularly. Necker can house 26 visitors, which cuts down the cost per head, although hardly to a bargain price. Often, couples rent the island just for themselves, moving from room to room as the fancy takes them.

Unlike a hotel, none of the rooms have keys, nor do they need them. You can eat and drink what you want, whenever you want, and do pretty much as you please, without any fear of running into strangers or paparazzi, not that I've ever found paparazzi to be a problem.

If you can't face the 200-yard walk from the beach to the house, a phone is always near at hand for you to call a car. If you find the sea just a little bit too warm, the temperature in one of the nearby pools is kept a few degrees colder. When bored with tennis, snooker, backgammon, chess, sailing, snorkelling, windsurfing and the inflatable banana, you can visit the nearby love temple for a quiet bonk (or even a noisy one). It consists of a very large bed on stilts.

But there are limits to the luxury. The staff talked proudly of how, at the last minute, they had been able to "source" a bottle of Chateau Haut-Brion 1978 for an earlier guest, but sadly my request for Iranian Sultanie vodka went unanswered.

It is an absurd life, one far removed from the problems of commuting on a Virgin train, but one you get used to absurdly easily, and you find yourself frowning when you notice that one of yesterday's champagne corks has not yet been removed from the beach.

And here are some that won't cost - or deliver - as much...

Private islands are not for everyone. An English couple who bought an island off the west coast of Scotland spent their evenings gazing wistfully at the lights on the mainland. Most mornings the husband would say: "I'm just going out in the boat," and he would head off to spend his lunchtimes in one of the dreariest pubs in the Highlands.

They, like most people, suffered from the delusion that there is a great party going on somewhere nearby and they haven't been invited. Successful owners of private islands are very different. They believe that any party they haven't been invited to isn't worth going to. That, too, is a delusion.

They are also, for the most part, barking mad. Typical owners include:

Dr Moreau who sought total privacy in the South Seas to conduct his beastly genetic experiments.
Hospitality rating: 0/10.

Dr No who sought total privacy in the West Indies to plot world domination.
Hospitality rating: 0/10.

Calypso and Circe in the Odyssey, who welcomed strangers to their alder-fringed islands in the Mediterranean, so long as they didn't make any plans to leave.
Hospitality rating: 5/10.

Lord Summerisle in The Wicker Man. Rather too warm a welcome.
Hospitality rating: 0/10.

Count Zaroff in the classic 1932 film The Most Dangerous Game. The perfect host until after dinner when he would amuse himself by setting his hounds on the guests.
Hospitality rating: 0/10.

The queen of Emain Ablach, the island of apples in the far west. In Celtic legend, Bran the son of Febal stayed for a year, entertained with every imaginable luxury, but when he returned home, he found that hundreds of years had elapsed. When one of his sailors jumped overboard, he turned to ashes the moment he touched the ground.
Hospitality rating: 8/10, but don't expect to make the flight connection on the way home.

Uncle Quentin on Enid Blyton's Kirrin Island. Lashings of ginger beer fail to make up for the high crime rate on the island.
Hospitality rating: 2/10.

The practicals

Necker can be booked through Limited Edition by Virgin, 5 The Lanchesters, 162-164 Fulham Palace Road, London W6 9ER (0800 716919, fax: 020 8600 0485). Renting the whole island costs $14,000 a day for 1-7 guests, rising to $29,000 for 20-26 guests. On special Celebration Weeks - September 5-12, October 7-14 and November 18-25 - rooms cost $13,000 per couple per week, master suite supplement $1,100, Bali Hi and Bali Lo supplement $1,925. Flights not included. Virgin Atlantic (01293 616161) flies London Heathrow to Tortola via Antigua for £2,218.30p premium class return, £814 economy.