It’s disco night aboard the RMS St Helena. Here on the 105m-long ship in the middle of the South Atlantic Ocean, somewhere between Namibia and Brazil, the sun lounge has been transformed into a dance floor. The barefooted wife of the King of Tonga’s chief justice boogies energetically with the South African geology professor while the Norwegian oil chemist drinks whisky at the bar until he is reeled into the conga line by the Australian insurance broker. The line snakes out of the door and past the saltwater pool where the Norwegian’s travel companions tackle him into the water, taking with them the professor’s wife and the British divorcee. The next day, shoes and clothes are reclaimed on deck and the RMS continues its journey at 16 knots towards St Helena, its first stop after leaving Cape Town on a 19-day roundtrip voyage.

The RMS St Helena is not a cruise ship. Operated by Andrew Weir Shipping, it exists to deliver mail and cargo and people to the British Overseas Territory of St Helena, an island of fewer than 4,000 British citizens who are pretty much stranded there (the ship’s journey will take it to Ascension Island, then back to St Helena before returning to Cape Town). It’s the most remote island in the world. It has no airport, no mobile phone service and this ship – one of the last mail ships left in the world – is their only link to the outside world.

The RMS was built 21 years ago to service the island; it carries 128 passengers, 56 crew, general cargo and 92 containers with everything from food and cars to live animals. Even though the original purpose of the ship was to deliver post, in the age of email it now normally carries only two and a half bags from the Royal Mail.

St Helena native Captain Andrew Greentree meets us on the bridge early one morning in his crisp white officer’s uniform complete with shorts and high white knee-socks. He has been with the ship for 18 years. “In the past, we carried 300 to 400 bags,” says Greentree, “but the decrease in the amount of mail we carry hasn’t affected us. Really, the main purpose always was to carry the cargo and the passengers backwards and forwards – and that’s what we still do today.”

The ship calls at St Helena an average of 32 times a year bringing home St Helenians (aka Saints) who live abroad or have been travelling, as well as delivering hardy British government workers and teachers who love the idea of a remote posting, along with tourists intrigued to see where Napoleon was exiled and died.

The fate of this ship, and its impractically long and wonderful sea journey to St Helena, will be sealed by the end of the year when the British government decides whether it will build the airport that has been promised to the island for more than 50 years. If it ends up being built, then this ship and the oddly endearing journey that entwines so many random lives will vanish. Monocle climbed on board to record what may be one of the RMS St Helena’s last voyages.

For many passengers on the vessel, it’s the trip of a lifetime. Despite the seasickness and threat of rogue waves (word of advice: don’t Google “ocean conditions around the Cape of Good Hope” before you leave), the remoteness of the place has made St Helena a mythical destination. Gwyn Bassingthwaight from the town of East London, South Africa, has wanted to come to St Helena for his entire life. “St Helena is one of those unknowns. It’s incredibly remote, if you think you have to spend five days on a ship just to get there. I have wanted to go ever since I collected stamps as a kid. St Helena always intrigued me. And there’s the most remote nine-hole golf course on earth, which I’m very excited about playing on. And I wanted to get here before they build the airport.”

“I knew nothing about St Helena before this trip,” says Oyvind Haugseth, a chemist from Bergen, Norway, with a wobbly grip of geography. “I thought it was in the Mediterranean. I came with a friend who is a tour operator in Cape Town and we’re going to do some scuba diving. I have the impression we’re going to be some of the last people to experience this trip and this culture.”

We leave Cape Town on a Friday afternoon after a stowaway search (none found) and an emergency drill in how to use the lifejackets that are stored under our beds. The passengers stand on deck making jovial conversation. Table Mountain gets smaller and smaller as the ship heads out. We will not see land, another boat, plane or bird or have any contact with the outside world (there’s no phone service or internet on board) until we land on St Helena the following Wednesday.

Before panic sets in, the distractions start. A note arrives under the cabin door announcing dinner at 19.30 sharp in the dining saloon with mess dress: nautical talk for formal. Several of my co-diners at the Captain’s table are too seasick to eat. Dinner is grand; the white-uniformed staff line up to greet passengers as they enter the dining room. The dinner is very British – six courses including soup, fish with heavy sauces, vegetables, roasted potatoes and treacle tart for pudding.

The cabins are immaculate and orderly. Even the seasickness bags are smart – crisp, white and oversized. But that doesn’t stop a lot of them being pressed into use. Each cabin gets assigned a steward, in my case a stewardess, Emma, and every morning she brings a small pot of coffee on a tray with that day’s edition of the Ocean Mail, the newsletter recounting the activities on board each day, including the dress code for the day and evening. Today’s events include a shuffleboard tournament at 11.00 Bingo at 13.30. Then a documentary called Discover St Helena and at 18.45, a captain’s cocktail party and dinner. Dress tonight will be black tie. The bottom of the newsletter says, “Ship’s clocks will be retarded by one hour at midnight.”

The days float together punctuated by Pavlovian meal breaks: breakfast at 07.30; beef tea at 11.00; lunch at 12.15; full English tea at 16.30; cocktails at 18.00; another six-course dinner at 19.30 in the saloon. On the deck, there is not much to look at but the expanse of steel grey water. The sound of the engine and the swoosh of the sea hitting the boat is hypnotising. With this much food inside you, it would be hard to be very energetic.

People are soon bored with their books and so you drink, and drink, and join in the games. Teams start forming early for the afternoon trivia quiz. The team with the oil geologist, the man who makes the chess sets and the ham radio operator are in the lead. Now the ice is broken. At dinner the drinks fly and the rowdiness factor increases. Captain Greentree explains what happens if someone dies on board (they store the bodies in the vegetable freezer). The Tongan judge wonders how the King of Tonga is still single at 62 even though he has three palaces.

The next morning, I find Oyvind, the chemist, on deck nursing a hangover with a black coffee, trying to make sense of last night. “It’s very bizarre. We had the Captain’s reception yesterday. You get this feeling of walking around in a living antique – the old Commonwealth Britishness, all the formalities with the uniform, the etiquette, and the properness. Then I was dragged into a round of that dog race. Then some threshold broke and everyone started dancing. And we had a drunken bath in the tiny little pool. I started it. Then everyone jumped in. It was a chain reaction of middle aged people in their clothes.” The rambunctiousness continues until we anchor at St Helena. Romance blossoms on board with some members of the Professor’s hideaway tour (28 passengers on a guided tour of St Helena led by Professor Colin Lewis).

Three Saints join me for breakfast, Colin, Valerie and Ella, and the conversation once again turns to the airport. “It would be good for medical purposes and tourism,” Valerie argues. “But it will probably ruin the island,” says Ella.

After losing in a game of deck quoits, I strike up a conversation with the man on the next lounger. David Taylor is a British architect who has been living on St Helena for two years as the island’s urban planner. He came over to ready the island for the airport. “No sooner had I arrived,” says Taylor, “and the British government suddenly put the airport project on hold. What they call ‘pause’. They had the tender back from contractors and the figure had come in at £350m [€396m]. That is a very significant sum of money for an island with 3,800 people. Then to everybody’s surprise, in July last year, the Cameron government confirmed the airport would go ahead subject to various conditions, one of which is to raise the activity level on the island by attracting tourism. But do it in a balanced way that doesn’t wreck the place.”

Even with the airport, Taylor thinks, “Most tourists will still want to go by boat. If the island offers anything it is its remoteness, its detachment and the romance of going by ship. And you’re on a bit of the island on the ship. It’s run by Saints. And it has a St Helenian feeling to it. But the food on the RMS is luxury by comparison. It really is a struggle to get fresh produce on the island.” We are interrupted by the crew who are clearing the deck in preparation for the big outdoor barbecue tonight on deck. Tomorrow we arrive in St Helena.

Approaching the island is everything the sea journey built it up to be. In anticipation, from 06.30 most of the passengers are on deck. On the horizon as the sun comes up all you can see is one slice of light between grey sky and grey sea. Rays of sunlight shoot down like spotlights.

All the while, the crew and passengers are as excited as little kids, running from one side of the ship to the other to see the island. At about 08.00, St Helena comes into full view. It is a relief to see land. As we sail closer, the clouds lift and the sun lights up the top quarter of the mountains. And then, as if on cue from the St Helena tourist board, a rainbow appears and then another one. The double rainbow drops in the bay in front of us. Not many islands could match that entrance. Soon after, we put on our life jackets, disembarking the ship to arrive at the sleepy capital Jamestown. We say goodbye to Rod and Elizabeth, and Nigel and Colin and Lucy, and the Schusters and Professor Lewis – not realising that we will see them regularly in the town. Every day. Everywhere.

Jamestown is a picturesque, one-road village nestled into a valley between two steep cliffs. The buildings are colourful and tiny and crooked. And the nature is dramatic – the sea cliff is divided by a 699-step staircase that people run up for fun – the record time is six minutes (well, what else are you going to do here?). Many people in the town meet the ship and spend the next few days on the dock going through the containers to collect their car parts, motorcycles, baby toys and industrial quantities of toilet paper.

This island was a key port of call for ships in the 17th century on the way from Europe to the East Indies. When the English East India Company took over St Helena in 1659 – and then again after some tussles with the Dutch in 1673 – the island was settled by English, slaves from the East Indies and Africa, and then another influx of English after the Great Fire of London. Which might explain the Saints’ unusual accent. They speak English, but it’s more like a cross between a Cockney accent and a 17th century pirate – sort of Eliza Doolittle meets Johnny Depp’s Jack Sparrow.

Owen James, an economist from London who has arrived on St Helena for a two-year posting, admits there is no financial benefit in Britain having this island. “St Helena exists on £30m [€34m] in subsidies a year from the British government,” says James. “The population has declined by 25 per cent in the past 10 years to about 3,800. But from an economist’s perspective, £30m is not a lot and the UK has a moral obligation to keep St Helena going.”

Everyone’s hopes here are on tourism, even though there are no beaches and only 38 rooms in the various inns. St Helena might attract eco-tourists because the environment here does live up to the hype. The several-hour-long drive around the 122 sq m island is breathtaking for many reasons, including the sharp hairpin turns and mountainous off-road conditions. There is a heart-shaped waterfall and palm trees, and flowering shrubs overlooking expansive sea views. But lush vegetation and Napoleon fanatics cannot save the island.

The plan, according to tourism development executive Mike Dean, is to increase tourism to 30,000 visitors a year up from the 1,200 to 1,500 a year who come now. He and his eight-person tourism team on the island just received £1.2m from the Department for International Development (DFID) to do this. Among many projects on the horizon, Dean says, “We’re looking to develop a series of boutique hotels that would be run by Saints.” Perhaps it would work. But David Taylor, the urban planner says, “Anyone with any get up and go has gone.” The young people are leaving the island in droves but there is hope that with the airport and outside development creating opportunities here, more Saints would come home.

Thomas Pynchon wrote Mason & Dixon about two astronomers who travelled to St Helena and went mad. It’s easy to imagine. On our last day in St Helena before getting back on the RMS for a three-day voyage to Ascension Island for an RAF flight back to England, we drive up a steep cliff to visit Nigel Cawthorne, the ham radio operator who travelled to St Helena to broadcast from here in Morse code. Cawthorne, in an anorak, greets us on the rainy hilltop, shouting over the howling wind, “Welcome to Ham Radio Heaven.” Grinning madly, he sits before his machines and taps out a message. “Look. There’s Japan. Croatia. Everybody’s jumping in!” he exclaims.

Watching this man on a hillside in the middle of the South Atlantic Ocean thrilled to be able to communicate with the outside world, I am reminded of what Taylor said when we spoke on the ship: “Everyone on St Helena is in some measure odd. And it has to apply to us, even if we don’t think it’s true.”