The gravel road unravelled through thickly forested valleys like a wayward strand of dental floss. As our minibus burrowed through the botanical mayhem, our guide, Percy, swiftly added another 70 bird species to our list – still only a fraction of the 1,000 species (about 10% of the world’s total) that are found in Manu Biosphere Reserve.

A single hectare of rainforest here can support more than 200 different species of trees. Add to that a similar variety of mammals and an ever-increasing inventory of reptiles, amphibians and insects, and you have the ultimate wildlife hot spot – more biodiversity than anywhere else on earth.

To reach the heart of this Eden, however, involves a three-day overland journey from Cuzco, Peru’s adventure staging post.

“So, Percy,” said Simon, as we reached our first night’s stop, a small wooden lodge snug in the cloud forest. “What’s out there that could kill us?” At barely 5ft tall, Percy was a good 18in shorter than my brother. His impish face took on a mischievous glint as he began to enthuse about deadly snakes; halfway through, he was interrupted by a piercing shriek. “Don’t worry,” he smiled. “That’s just a bamboo rat – this big.”

“Christ, there are rats the size of cats here,” said Simon, as we retired to our cabin, the beam from his torch chasing shadows through the forest. He looked apprehensive – but then he’d always been far more excited about our actual journey than the wildlife along the way. He was no David Attenborough.

After two hours of driving the next morning, we finally emerged from the hills into an area of sparse settlement, where the forest edge gave way to random plots of banana, manioc and coca. At the jungle-frontier village of Pillcopata, we stopped for warm beers and a chance to stretch our legs. Outside it was 90 degrees in the shade, with humidity to match. Occasionally, an old truck with wrecked suspension trundled past, or someone would shuffle across the settlement’s single, dusty street. Pillcopata was like something out of a Mad Max movie. There were even bottles of pickled snakes at the local bar.

Simon was in his element. When we took a canoe across the river at nearby Atalaya and found a 1967 Land Rover waiting to transfer us to our next lodge, he could barely contain himself: “Look, it’s even got the original Solihull badge on the back!” With wires hanging from its dashboard like the entrails of a decapitated animal, the West Midlands wonder fired first time and jolted us a mile or so to the converted homestead of an old tea plantation.

Within minutes of our arrival, Percy was leading us off on a jungle hike. We stumbled through spiders’ webs as we tracked squirrel monkeys flitting through the canopy, 90ft above our heads, before climbing a rickety tower for a monkey’s-eye view. According to Simon, it was one of life’s “epic moments” – braced atop a scaffolding nightmare, gazing across the treetops of the Amazon. And I would have agreed with him had the sweat bees not chosen to share it with us. Our next destination was six hours away by canoe: Manu Wildlife Centre, a cluster of thatched cabins cowering beneath the soaring trunks of rainforest giants, is located near several of the reserve’s prime wildlife-watching sites – most famous of which is the macaw clay lick.

Before dawn, we slipped through the forest to a hide overlooking a low, sandy cliff eroded into the river bank opposite. As sunrise inflamed the forest canopy and sent tendrils of mist squirming across the water’s surface, we noticed something odd about the trees. Several of them were bare, and what we had originally taken for leaves were actually parrots – hundreds of blue-headed, orange-cheeked and mealy parrots.

Like a stained-glass window exploding, they simultaneously took flight and streamed overhead, their whirring wings and high-pitched squawks shattering the predawn calm. As the parrots settled on the bank and began nibbling the clay (which, according to Percy, helps to absorb toxins in their fruity diet), the first macaws arrived, their raucous cries adding to the avian hullabaloo. The vegetation overhanging the river bank became daubed with red, yellow and blue, as a hundred or more scarlet macaws joined the noisy, colourful ritual.

“There were a lot of parrots, that’s for sure,” said Simon, trying hard not to appear too moved. I’ll make a twitcher of him yet, I thought.

But his whole experience – the epic journey, the sense of having reached somewhere truly remote – was about to be dealt a blow. Flying in by light aircraft, a group of 23 elderly (and talkative) Americans had arrived at the lodge, each one wearing a name badge emblazoned with Wheaton District Council Leisure Centre.

“Is no wilderness sacred?” said Simon, whose mood only momentarily perked up when one of the new arrivals became trapped in her cabin by a territorial blue throated piping guan – a bird about the size of a turkey, but with the temperament of a pit bull.

Needless to say, Simon leapt at Percy’s suggestion of spending the night sleeping rough in the forest, away from the lodge. A two-hour walk led to a raised wooden platform overlooking a trampled clearing that Percy told us was frequented by tapirs – a largely nocturnal mammal. Sitting on mattresses draped in mosquito netting, we ate our packed dinners and waited in silence.

Night fell quickly. The techno babble of insects, frogs, owls and nightjars built steadily, each creature doing its best to imitate a digital alarm clock. Not that sleep was possible. Percy switched on his torch (muted by a red filter) and the macabre light picked out several large shadows fluttering above the clearing.

“Vampire bats,” said Percy. There was a long pause. Then I heard Simon exhale. “Percy, did you just say vampire bats?”

“Yes, the big ones.” There was something disturbingly frank in the tone of our guide’s voice. I heard Simon fidgeting with his mosquito net. Then Percy flicked off the torch and plunged us into darkness again. After three hours trapped in our ghostly cocoons by circling vampires, and with not so much as a sniff of a tapir, we gave up and returned to the lodge.

Ironically, we saw two tapirs bathing in the river the following morning. It was a fortuitous start to an excellent final day in Manu. Hiking to a nearby oxbow lake, we spent hours paddling a dugout canoe through pristine rainforest reflections, pausing to watch jacanas tiptoe over lily pads or howler monkeys feed in the surrounding forest. We even spotted a three-toed sloth in a fig tree.