If first impressions are so important, what to make of an island where the luggage from the twice-weekly flight takes more than an hour to come through because the drugs are unloaded first? Where locals greet each other in arrivals by kissing noses and bobbing their heads like courting swans. Where lines of vultures stand where the taxi rank should be, as if waiting for a fare. Where the drive from the airport takes you past goats wearing condoms and through a fertile moonscape of plants that look like sci-fi monsters and space hoppers. And where a sign in your guesthouse room asks you to refrain from opening your curtains as your neighbour will be offended if he catches you looking into his yard.

To say that first impressions of Socotra, a 3,625 sq km island planted in the Indian Ocean like a big pair of puckered lips, offer just a hint of otherness, would be like saying that Darren Day offers just a hint of the cad.

For at least 20 million years, since it split off from the Horn of Africa, 170kms to the west, and Yemen on the Arabian peninsula, to which it belongs, 500kms to the north, Socotra has been cut off from the world in every sense. Indeed, my week-long journey to the island had only served to emphasise this isolation. From Yemen's capital, Sana'a, we had driven overland through Marib - where my Kalashnikov-wielding guards were a reminder of recent tourist kidnappings - then through the vast Empty Quarter. At Shibam, whose astonishing mud skyscrapers led 1930s English adventurer and photographer Freya Stark to christen it the 'Manhattan of the Desert', we dropped down the Wadi Hadramawt to the tiny airport at the coastal town of Al-Mukalla, from where we could catch a 50-minute flight across the Gulf of Aden.

Socotra's airport was built in 1999, but even now, for four months during the vicious south-west monsoon that arrives in May when hurricane-strength winds whip the island mercilessly, ships cannot dock and planes struggle to land. In 2005, just 400 foreigners came.

For centuries the islanders existed in harmony with a fragile ecosystem. They took only the fish they needed, used plants for every conceivable purpose, tended their goats and, in the mountains - where the majority still live in caves and light fires by rubbing sticks together - collected rare aloes, frankincense and myrrh to be despatched to the Gulf states. Until 1990, the island had a barter-only economy, many people still used red-hot metal bars to exorcise illness and the last 'witch' was tied to a board and given a sink-or-swim ultimatum in the late 1960s.

But its very isolation threatens to be Socrata's downfall, for it is not only the culture that has existed in a vacuum. The island's flora and fauna consists of weird and wonderful species long extinct on the rest of the planet. Indeed, the 300 species of plant, 24 reptiles, 113 insects and six birds endemic to Socotra have led some to dub it the new Galapagos.

It also has miles and miles of pristine white beaches, its position as an oceanic crossroads gives it world-class diving potential, and the crushingly poor population has, through television, recently been made aware of the party going on in the rest of the world. It is, as developers might say, 'ripe'.

A Unesco Man and Biosphere designation in 2003 was meant to protect the island, but the rapid rise of previously unknown land disputes, commercial fishing by foreign fleets and the impending opening of Socotra's first 'international' hotel, complete with Thai masseuses, only adds to the feeling that disaster looms.

That first morning, we set off west from the capital Hadibo, bumping along rutted, unmade roads on the springs of our Landcruiser. I was travelling with Kate Phillips, who was on a recce trip for High & Wild, a UK tour operator which started selling Socotra as an eco-destination last year. Also in the car were Abdul, our guide, a grandson of the last sultan, and Noradeen, our driver, left cheek permanently swollen with qat, the narcotic privet-like leaf that descends from the skies on Tuesdays and Fridays to scenes of frenzied excitement in arrivals.

We passed through dusty coastal settlements where squat stone and coral houses with palm-thatched roofs hunkered in perpetual readiness for the winds. Women shrouded in black stood statue still. Children tumbled out of doors and windows like bees from a hive to shout and wave. If we stopped and got out, they would freeze, then flee in terror, doors slamming behind them.

Many of the 40,000 inhabitants speak only Socotri, a language unknown to the rest of the world but believed to have its roots in Sabea, the Queen of Sheba's ancient city state on the southern Arabian mainland, from where, around 1,000BC, the first settlers were believed to have come. Socotri still has no words for things that are not found on the island, so to describe a dog or an aeroplane, Socotrans have to borrow from Arabic.

That Socotri has no written form makes the island's exact history tricky to pin down. But a succession of colonists and opportunists - from ancient Egyptians, Greeks and Romans, to the Portuguese in the 16th century, the British in the 19th and the Soviets in the 20th - tried their luck on Socotra. All, due to the weather, the isolation or, in the case of the Portuguese, a bloody battle with the Bedouin, left behind a few genes and little else.

We cut inland across the plains, flecked with croton trees bent in perpetuity, and crossed the limestone plateau heading towards the Haggier Massif, a saw blade of granite pinnacles with cloud halos that dominates Socotra and culminates in the 1,570-metre Jebel Skand. As we climbed, the first exhibit in Socotra's botanical freak show appeared. The desert rose, with its grotesque elephantine trunk for storing water and a tiny mop of foliage, looks like some exotic anemone that would be more at home on a reef. After the monsoon rains, in sheer relief, it explodes into flower, turning whole hillsides pink.

Then came the forests of wild frankincense trees, where Abdul scored a trunk with his knife so that the opaque white sap gurgled out. The ancient Egyptians, who believed frankincense helped spirits to reach the afterlife, are thought to have travelled to Socotra 4,000 years ago to farm the trees that to them would have been more valuable than gold is to us today. Ancient Egyptian inscriptions mention Terraces of Incense and there are a number on the island, dusty and forgotten, their origin and purpose unknown to Socotrans.

We parked the 4x4s and started a trek into the Haggier, accompanied by four Bedouin porters. We walked through the gentle uplands through clumps of red aloe and acacia trees, past camels and dwarf cattle and vast herds of goats, some wearing comical apron-like cloth condoms. Abdul explained that this is to ensure that kids are only born during the rainy season, when there is plentiful grazing.

After an hour or so, we saw our first dragon's blood tree, Socotra's iconic plant with a distant cousin on the Canary Islands as its only relative. Like an enormous umbrella blown inside out, it grows along the ridges and in forests on the limestone plateaux.

The dragon's blood tree gets its name from the rich scarlet sap that oozes from its trunk when cut. Trading the waters of the Arabian Sea, the Romans used to pop into Socotra to pick up a pint or two, the sap being much in demand from gladiators, who used it to disinfect wounds. Today, Socotrans use it as make-up and to decorate their clay pots.

We stopped at a cave, where Damak, a wizened-old goatherd, lived with his extended family. Inside, thick with wood smoke, a distended goat skin complete with four stumps, used for churning milk, hung from the ceiling like the animal balloon of a children's entertainer. We drank tea infused with cinnamon and a quantity of sugar that would make a builder balk.

Further on up the trail, Seid, the head porter, dived like a goalkeeper into the waist-high spleenwort and emerged cradling an extremely cute brown baby goat. 'That's a cute kid,' Kate and I cooed.

Seid certainly thought so. In fact, he threw it into his sack, as casually as if he'd just plucked an apple from a tree, and marched off, trailing in his wake a pathetic muffled bleating and leaving us, and the kid's mother, in states of, respectively, mild and acute distress.

That night we camped at 1,300 metres, under the brooding shadow of Jebel Skand. The goat was dispatched, skinned and within 15 minutes of its last bleat I was eating its liver, then its intestines, then the choice cuts. All that was left, discarded in the embers, were four little hairy brown legs. A dozen handsome Egyptian vultures stood by, insouciant but attentive, like waiters trying, as if by will, to get the last diners to leave.

As the moon rose, the porters, in ghostly silhouette, headscarves blowing in the breeze, chanted and prostrated themselves towards Mecca. Far below us, washed in the pale light, the forests of dragon's blood trees looked like an invading army of paratroopers.

Back around the fire, Seid played a copper flute and the other porters began to sing, an adenoidal wailing that sounded like a record being played backwards. 'What are they singing about?' I asked Abdul.

'Goats,' he replied.

Next day we drove along the north coast, with its 20km-long beaches where loggerhead turtles come to nest every summer and white sand dunes hang like vast awnings from the granite bluffs. We parked and walked for a couple of hours, up through boab trees, wild pomegranate and candelabra-like euphorbia. Abdul pointed out some of the endemic birds: the Socotra starlings, tiny Socotra sunbirds, with their long nectar-gathering bills, and the imperious Socotra buzzards dancing like kites on the thermals.

We stopped at a pool in a wadi, where a Bedouin was busy hand-fertilising his date palms, and stared into the crystal water, full of strange orange crabs unique to the island that are found up to half-a-mile above sea level. Iridescent dragonflies swooped and hovered, and Abdul explained that many of Socotra's endemic insects have evolved short, frantic wings to stop them being blown out to sea by the monsoon.

We arrived at the mouth of the Huq cave - as vast and as exalted as a cathedral - and plunged into the darkness, feeble torches picking up the yellow stalactites and stalagmites like giant Twiglets covered in custard. On and on we walked, for two kilometres, maybe three, passing petrified coral forests, the floor falling and rising. Abdul explained that clay pots and Sabean inscriptions have been found six kilometres inside the cave, left by a family extolling, in Garboesque terms, the virtues of solitude.

That night, we camped on the beach, deserted save for bleached whale bones and thousands of scuttling ghost crabs. In our million-star restaurant, we reclined on goat-hair rugs and ate a rock lobster, whose journey from life to my stomach was even briefer than the kid's.

We spent the next few days driving along the coast, stopping to swim with bottlenose dolphins or snorkel on the sumptuous reefs, where huge coteries of grouper and parrot fish, curious and unhabituated to people, follow you like some aquatic Pied Piper. At Ditwah, a toothpaste-coloured palm-fringed lagoon, where juvenile stingrays the size of ping-pong bats made for watchful paddling, we ate kingfish and watched the sky catch fire with the intensity of a Renaissance painting.

At Qalansiya, on the western tip of the island, we took a boat ride with a fisherman past columns of Socotran cormorants, still as fence posts on the cliff shelves. Overhead, brown boobies and grey herons flew, while spinner dolphins performed stunning acrobatics around the boat. At Showab beach, we found where Flipper goes when the final show is over; dozens of carcasses lay on the sand, rotting and putrid yet still smiling like troupers.

On my last evening in Socotra, as I wandered with Abdul among the mud brick houses of Hadibo, goats devouring cardboard boxes, 'Allah is Great' wafting along the dusty alleyways, I asked him what he thought the future held for the island. 'We are very poor and can offer much to eco-tourists like yourself,' he said. 'But we don't want mass tourism. We know it would destroy our lives.'

He ushered me towards a door, from where the sound of drums was emanating. Inside, the Friday dance was in full flow. Burqa-clad women, ululating wildly, were spinning like demented bats, kicking up clouds of dust. The men, cheeks swollen with qat, eyes bulging, danced in line formations; the Africans of the coast, the Arabs of the plains, here and there blue eyes and red hair, the flotsam and jetsam blown to Socotra down the ages through accident or ambition. I was the lone tourist. I turned my digital camera to black and white and looked at the screen. It was Freya Stark's Arabia.

Essentials

Mike Carter travelled with High & Wild (www.highandwild.co.uk; 01749 671777). A 17-day group trip - eight days on mainland Yemen and nine days on Socotra - costs £1,285pp - £1,725pp depending on group size. Price includes meals, hotels and camping, transport and guides but not flights. Tailormade trips are available for two people or more. Yemenia (020 7323 3213; www.yemenairways.co.uk) flies to Socotra twice a week from Heathrow via Sana'a, with fares from £452.

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