Keene views their venture as offering a vacation with a difference, combining adventure travel with community development. 'The tribe will benefit from an experience that is so much more than just a week's holiday on an island,' he says. 'The global tribal community will have a purpose - to develop an eco-community in a real place. That challenge will bring rewards as the tribe will be empowered to take part in something rather than simply be guests.'

Keene and James, both 26, also hope the project will benefit indigenous islanders as jobs are created, and visitors buy locally produced food and goods. The organisers will also contribute to an education fund for the island.

The pair met online in December after James, a TV industry gopher, came across Keene's travel website, careerbreakcafe.com. James had been 'looking at trends in online communities and online ideas, and at how that could be taken offline into real space, a real place', while Keene was interested in sustainable development, having run volunteer projects in West Africa.

Inspiration hit after James read a travel book about islands. 'We went about island hunting, which is difficult to do when you don't have any money. So we posed as island brokers,' says Keene. Eventually, they were introduced to Vorovoro and to Tui Mali, chief of the Yavusa tribe. Tui Mali, his brother and their families are the sole inhabitants of Vorovoro, with the rest of the tribe living on a nearby island. The chief didn't want to ally himself with resort operators, fearing his cherished home would be turned into a monstrous luxury complex. But after talking with the partners, Tui Mali agreed to lease the island to them for three years.

Keene and James, also known respectively as Chief Bengazi and Chief Marika, launched tribewanted.com and started flogging memberships in three tiers. Nomads pay #120 ($1,700) for one week's stay, while Hunter memberships cost #240 for two weeks, and Warriors pay #360 for three weeks.

They expect to raise about #1 million. The fee covers the cost of accommodation and food, but tribe members will have to pay for their flights and other transport to and from the island.

So far, about 400 people have signed up and the first visitors will start arriving in September.

While Keene hopes to attract 5,000 members, he says they don't need a minimum number in order to proceed. 'The difference between 500 tribal memberships and 5,000 is the amount of money to develop the islands. Let's say for some strange reason we didn't sell 1,000 places. We'd still be able to run the project but we wouldn't be able to do the amount of development, or the number of projects that we want to.'

Only 100 tribe members will be allowed on the island at one time. Billed as '200 acres [80 hectares] of cliff-topped jungle and palm-fringed paradise' set in the South Pacific, the long, skinny island is near Cakaulevu Reef, the world's third-biggest barrier reef. It offers excellent scuba diving opportunities and there are also good surfing spots, Keene says.

Those looking for an adventure in the style of popular TV shows such as Survivor or Lost won't be disappointed. But hard work is required, especially in the beginning - there is no running water or electricity on the island.

'For the first tribe members, there will be nothing there but toilets. They will have to help build accommodation,' Keene says.

A broadband connection will also have to be set up, so members elsewhere can track changes through the Tribal TV channel. Tribe members are encouraged to participate online throughout the life of the project. For example, in the run-up to September, they will vote on the design for the village buildings the first visitors will construct. They'll also vote on a new name for the island, as well as tribe leaders, who will get an extra month's stay in return for helping to run the community.

However, most of the day-to-day decisions will remain with tribe members, and it will be up to them to decide how the community evolves, Keene says. 'There's all these interesting sociological questions that we'll ask the tribe. Democracy is probably not the right word - probably participation.'

The founders hope to attract a diverse crowd, including people on gap-year or career breaks as well as builders, architects, surf instructors and marine scientists.

So far, most tribe members are British, with a smattering of Americans, Canadians, French, Dutch and other western Europeans. But Keene also wants to get the word out to other non-English speaking countries, including the mainland.

'We're hoping we can have a United Nations of tribe members, but it's up to whoever signs up first,' Keene says. 'China is as much involved with [online communities] as the US and Europe.'

Lara Jefferies, the daughter of outgoing Hong Kong Ballet artistic director Stephen Jefferies, is saving up for a Nomad membership. Now based in London, the 23-year-old is attracted by the quirkiness of the project, which she views as a good substitute for the gap-year volunteering that she never undertook.

'When you're working you only get two or three weeks [of vacation] and it's not very convenient to go out and work on a coral reef,' says Jefferies, a public relations executive.

'It's a fantastic solution for people who want to make a difference. People don't realise what a massive project it's going to be, but for me it's part of the excitement. It's not your usual holiday where you get looked after,' says Jefferies, who lived in Hong Kong for seven years after her father took up his post with the ballet company.

With the tribe 'you make it what you want. It's not something that has been done before', she says.

The project is definitely uncharted territory, and while the founders are hoping for the best, it's not hard to imagine things going wrong. What if tribe members turn on each other, and the venture degenerates into anarchy? Many have drawn parallels with The Beach, the Alex Garland novel about a backpackers' community in an idyllic Thai hideaway that becomes a savage nightmare.

As one Daily Express writer commented, 'If the project takes off, Ben must also be hoping that, unlike in The Beach or Lord of the Flies, his paradise doesn't turn into a living hell'.

Keene insists that won't happen. Unlike 'one of those Utopian island stories that goes wrong, this isn't an accident,' he says. 'It's not a plane crash, this is a structured tourism project.'

Besides, visitors will only be on the island for three weeks at most. 'For people to get angry or hacked off, they need to stay for longer,' he says. As in any community, there will be disputes. But Keene says other tribe members following the action on the website will encourage people to get along.

At the end of the three years, it will be up to Tui Mali and his clan to decide if they want to continue with the project, and whether to do so by themselves, in collaboration with the founders, or with another partner. If not, the village will be dismantled, leaving only footprints on the beach.