The last working Royal Mail ship is to cease operations when an airport opens on the Atlantic island of St Helena in 2012.

In the week that the ship - RMS Helena - embarked on its 100th voyage, four consortia competing to build the airport have been invited to visit the island to launch their bids.

In a referendum, the 3,800 islanders voted heavily in favour of the airport - and the chance to put the island back on the map with the biggest story since Napoleon died in exile in 1821 after six years on the windswept rock 1,200 miles off the west coast of Africa.

"We hope that the island will become self-sufficient after the airport is built," said outgoing governor Michael Clancy. "The potential growth of tourism is considerable but the ship can only carry a maximum of 128 passengers, which puts a limit on development."

Fewer than 1,000 tourists currently visit the island via RMS St Helena annually, with a further 1,500 on sporadic cruise ships - the government hopes for 10,000 tourists by 2017. But many fear that the island will sell its soul by looking to tourism for economic salvation.

Writer Peter Hughes visited two years and says of the airport: "It will change the island irretrievably. When the St Helena Herald broke the airport news, its second story was that the Bamboo Hedge Piggery had produced its first litter by artificial insemination. Such guileless days may well be numbered."

The island's government estimates it will need 250 rooms to accommodate visitors by 2015, and says there is scope for "one or two" flagship developments. More roads, power, waste management and water will be needed while the government is also looking for investors to build take-aways, shops and other tourism-related enterprises.

Three airlines have been invited to present their proposlas for service to the new airport, which will be able to handle Boeing 737-800 or Airbus 320 aircraft carrying 160 passengers.

But despite the massive upheaval, the government's prospectus insists it is looking to minimise the impact of tourism. It adds: "St Helena's natural and built enviroment is a vital part of its tourism offer and must be preserved. Each development... wil be subject to an enviromental impact assessment."

The RMS Helena has served the island since 199, and is the only way to visit St Helena. Most trips originate in Cape Town but one or two trips a year start at Portland, Dorset. Fewer than 90 sailings now remain until the ship is retired.

"The ship is our lifeline and the 100th voyage is a landmark. It is not a cruise but a special experience," said Kedell Worboys, the UK representative of the St Helena Government.

RMS Helena next leaves Portland on October 5, drops anchor at Tenerife and Ascension Island, and arrives at St Helena on October 19. It leaves for Cape Town on October 28, arriving there on November 2. A package of voyage, nine nights’ B&B on St Helena and return flight from Cape Town to the UK costs £4,883pp - book via Andrew Weir Shipping

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