In the mid-1920s, a curious figure turned up in south-west London. He had emerged from one of the harshest and most isolated regions of the Empire: the Rupununi Savannah of British Guiana. There, he had owned a ranch that was not only the largest in South America but the largest in the world. Here is his tale.

Harry Prideaux Colin Melville was born in Jamaica, in 1864, the son of a Presbyterian archdeacon. Unlike his father, however, Harry had never had an appetite for matters spiritual, and preferred the sight of gold. At the age of twenty-seven he decided to extract himself from Scottish Jamaica, and set off in search of ore. His gold-washing brought him to British Guiana. There, in 1891, he plunged into the forest, and was soon cooking up a case of malaria. At the moment of death – the story goes – he was found by some Amerindians. Harry had no wish to die in the dark, and asked for help to reach the light. With either payment or pathos, they agreed, and brought the dying Scot out onto the Rupununi Savannah. There, he liked what he saw and lay down to die.

Death on the savannah had suited Harry well. The next thing he knew, the grass was his home. He acquired two Wapisiana wives and settled down to become a trader in the finest fish hooks and trinkets. It was good business, and – after twenty years – he was the most powerful man on the savannah. Not only was he now the father of ten children, he was also a cattle baron, a district commissioner, and the Laird of Dadanawa. It was the largest ranch in the world, and covered an area about the size of the Lowlands of Scotland.

‘HBC’, as he now called himself, had arrived. All Dadanawa needed was some sort of link to the rest of the Empire. On cue came the First World War, and a surge in demand. British soldiers would march to Berlin on Rupununi beef. It was an appealing image, and the funds flowed in. By 1917 Melville had begun work on one of the most ambitious private trails in the world. Soon, Dadanawa would be pumping cattle up into the heart of Guyana, and then off to the coast. Or so he said.

Dadanawa is still there, and life carries on much as it did in 1923.

Seventy miles from the nearest town, it sits on a rise by the Rupununi River. At the top of the hill is a large and shady Brazil nut tree. All around it are the ranch buildings, and the peeling grandeur of Melville’s design. There are several workshops and saddle stores; barracks for the cowboys (or vaqueiros), slung with rows of hammocks; an abattoir; a tannery; two kitchens with huge ranges, and drying-lines dripping with buttery tripe; half-a-dozen water-towers, and an ancient wind-pump that sometimes stuttered and stopped; a small brick cottage for the foreman, and the enormous wooden halls of the management – all finished off in the Melville livery, balance-sheet white and Highland green.

Even now, the ranch is an enchanting place. It is not just the livery and the lovable staff, and the distant blue hills, melting together. It is the sense of a peculiar past, all around. The guest room is high up on stilts, and looks as if it has been quietly – and elegantly – flaking away since the First World War. Then there is the manager’s house, which is like the officers’ mess of an Edwardian army. Around the walls, there are weapons and saddles, and, at sundown, everyone sits on the balcony, drinking punch. As the ranch no longer has electricity, guests soon find themselves in the dark, and beginning to itch. ‘Time for dinner!’ says the ranch manager, and everyone fumbles their way downstairs. There, they sit in Melvillian splendour, dining on tablecloths adorned with his crest. During dinner (perhaps three great courses of soup and mutton and chocolate mousse) the bats come wheeling in through the windows, and squeal around the diners’ heads.

Even better, though, is the ranch store. This is the place to buy a stirrup, or a beer, or a single cigarette. At night, people gather here to listen to the distant crackle of the BBC, or for the cook – armed with a needle – digs the jiggers from their feet. But, as well as a bar and a clinic, the store is also the repository of almost a century of grassland junk. There are jaguar skins, giant fish skulls, several antique guns repaired with tape, a truncheon, a pickled snake, and endless Land Rover parts, going all the way back to 1950. Even things too big for the store are never thrown away. Just behind it is a collection of old army trucks, now green and hairy, and reverting to soil.

Every morning the cowboys assemble at the store. There are fourteen in all. With their long knives, El Greco faces, and leather gaiters – clinking with buckles and spurs – they are like some ancient, barefoot cavalry. Scowling and spitting and shooting blasts of snot, they look impressively dangerous. I once watched them kill a calf. Their knives descended on it like a shoal of fish, and swam around through the trembling flesh until suddenly everything was gone. It is said that Wapisiana men liked their women like this, with razor-sharp teeth filed into points, just like piranhas.

Once I went to watch them, out in the corral. There was a bonfire for brands, and – high up in the rails – the boys clambered around, waiting for their moment to drop down and join the fight. Below them, in the arena, hundreds of animals swirled round, blind with dust and mad with panic. Whips, forty feet long, sizzled over their heads, hissing and crackling like gunfire. Then the vaqueiros dropped, knives drawn. What followed was not so much sport as medieval warfare. Horn and withers became tangled in rope, and – amidst the bellows of terror – the knives began to dart around, nicking ears and emasculating bulls. At one point, a steer seemed to explode from the melee, and, like some huge and bloody meteorite, smashed through the rails and took off, over the savannah. No one seemed to notice that they had almost been killed. Even when the work was finished, the vaqueiros were not. Each found himself a furious steer, jumped on its back, and then rode it for a few exhilarating seconds, before the animal bucked him off.

‘What can I do?’ said the manager. ‘It’s the only life they know.’

I didn’t see the vaqueiros again after that. By my last day they were far away, rounding up distant cattle. Across the ranch, they still have over a million acres to cover. Whilst Dadanawa is not what it was in Melville’s day, it is still twice the size of Suffolk.

HPC had, however, long-recognised that size was not the issue. The problem for Dadanawa was – and is – an old one. Being hundreds of miles from civilisation, it is one of the most inaccessible spots on the continent. Cows still have a long way to go before they are beef.

In 1923, therefore, Harry cut his losses, sold the ranch to some gullible investors, and slipped away. It was years before his purchasers realised their mistake. Melville had even diddled them on the number of animals and the quality of grass. As for the cattle trail, it was a gruesome failure. At the first attempt to use it, over seventy percent of the animals simply vanished in the forest. Dadanawa only had a moment of prosperity in the thirties. Then came the age of the plane, and, in 1953, the trail was closed for good.

Meanwhile, Harry was long gone. Having abandoned his wives and children, he fled to Twickenham. There, he married for a third time, a nurse called Ethel Barker, and the couple settled down. Suburbia was a strange choice for a man who had spent so much of his life owning the horizon. But then, in July 1927, for the second time in his life, Harry Melville died. He was rich, sixty-three, and intractably malarial. This time, he was carried to Richmond Cemetery, and has never been heard of since.

It was not quite the end of the Melvilles, however.

His semi-feral children had produced plenty of brats of their own. Evelyn Waugh had met several of these grandchildren, when he walked through the Rupununi Savannah in 1933. Waugh disliked most children but to him the Melvilles were particularly beastly. And he may have been right. By 1969 the same grandchildren were numerous and boisterous enough to start a revolution. They rose in revolt, and declared independence from Guyana. But the Republic of the Rupununi lasted only a day before the Guyanese army appeared, and chased most of the Melvilles off into Venezuela. These days, not much remains of Harry’s world, except a handful of thready descendants, and, of course, the ranch at Dadanawa.

John Gimlette is the author of Wild Coast: Travels on South America’s Untamed Edge, Profile, £8.99

If you fancy visiting the Rupununi Savannah, contact Claire Antell, the Wimbledon-based representative of Wilderness Explorers on 020 8417 1585. (www.wilderness-explorers.com)