Freddie Flintoff's extraordinary 1,200km bike ride through the heart of the Amazon rainforest

The former England cricket captain always considered himself an environmental sceptic – until, that is, he joined the writer Robert Penn on the epic and gruelling bike ride

Rob and Freddie on the Trans-Amazonian Highway, near Jacareacanga (Rob Penn/Indus Productions)

The Amazon was never on my bucket list of places to go for a bike ride. The roads are poorly maintained, pounded by logging lorries and often mind-numbingly straight; the heat and humidity are debilitating; the scenery hardly changes for some two million square miles; and there are 196 species of snake. However, the chance to make a TV documentary about the rainforest with one of my cricketing heroes, Freddie Flintoff, was more than I could resist.

For a month last autumn, we pedalled along perhaps the most controversial road in the world to examine its environmental impact. The Trans-Amazonian Highway was built by the Brazilian military dictatorship in the early 1970s, to open up the southern Amazon basin for colonisation and economic exploitation. The government grandly claimed the 4,000km road would be "the last wonder of the world in the 20th century" and the first piece of a new South American transport network. Under the "land without men for men without land" scheme, 100,000 families were to be re-settled along the highway, from agriculturally poorer parts of Brazil.

Promises the government made were broken from the start. No more than 10,000 people were relocated, and they were quickly left to fend for themselves. The road was never even finished: it was never paved and it simply stops in the middle of the jungle, at a small town called Labrea beside the Purus River. The highway abides, though, as a red scar through the rainforest and a metaphor for everything that has gone wrong in the Amazon in the past four decades.

Freddie was a self-confessed environmental sceptic when we started; he doesn't even really like cycling. But he has a big heart and he can do a mean Elvis impersonation. He was motivated to visit the Amazon by his young children, who learnt about the plight of the rainforest in school. I'm an old-fashioned tree-hugger, and having ridden a bike round the world, the TV commissioners knew at least one of us could fix a puncture.

The highway starts in the east of Brazil and runs due west across the states of Maranhão and Para to Santarem on the mighty Amazon River, before veering south. We started cycling in the town of Itaituba, on the banks of the clear-watered Tapajos River. The plan was to cycle 1,200km, to the end of the road. Along the way, we'd meet gold-miners, cattle ranchers, legal and illegal loggers, sawmill owners, rodeo-bull riders, shopkeepers and schoolkids.

We rode no-nonsense, steel-framed expedition bikes, with no suspension and large, 29-inch wheels, manufactured by the British company Genesis. We took spare tubes, tyres and spokes plus a handful of tools. Freddie questioned the wisdom of taking bikes without suspension, but when you're thousands of miles from a bike shop, you want a steed with as few working parts as possible. Over the month, there were punctures, a shredded tyre, broken water bottles and a few minor adjustments to cables, but considering the condition of the road and the daily hammering the bikes took, they stood up remarkably well.

The cycling was hard from the start: 500m out of Itaituba, the tarmac turned to dirt. In places, the road was maintained and well graded, but for long stretches, it was no more than a cart track. Every time we passed a vehicle, we were consumed in a cloud of dust and had to ride blind for several, unnerving seconds, but we were continually stirred on by yells of delight from the side of the road. "They're just surprised," Freddie said. "There can't be too many idiots cycling here."

There are few communities along the Trans-Amazonian Highway: most nights we either camped in the jungle or beside one of the dilapidated, old roadhouses. We washed in the creeks and rivers, checking carefully for freshwater stingrays before plunging in. It was rough travelling. I wasn't sure how a former cricket captain of England and now part-time celebrity would take it, but he never lost his sense of humour.

"This is living the dream, eh, Rob?" Freddie said every night, as we hung our hammocks. One morning, as we packed up camp in the village of Sucunduri, Freddie disturbed a tarantula in the top of a rucksack. After that, we zipped all our bags at night.

Every four or five days, an electric storm burst over us, bringing respite from the blanket of heat and humidity. But while the rain tamped down the dust, it also turned the dirt to a gummy mud, which made pedalling even more arduous.

Approaching the town of Apui, our halfway point, the hills flattened and clouds of smoke blackened the sky in all directions, where deforested scrub was being burnt off to sow grass seed. Legally, landowners in the Brazilian Amazon are required to retain forest on 80 per cent of their property. Few do. Agriculture requires wholesale forest clearance, and ranching is the greatest single cause of deforestation in the Amazon.

"What would you rather have, beef or trees?" Freddie asked me as we approached Fazenda Macil, a vast cattle ranch near Apui managed by Jose Lucio. For me, the answer is trees, but we stayed with Jose Lucio for two nights and it was hard not to admire his pioneering spirit.

Travelling under the auspices of the Sky Rainforest Rescue project, run by WWF in the western state of Acre to promote agricultural initiatives that leave the trees standing, we began to find small signs that the global importance of the Amazon rainforest is also being recognised locally. We spent a day with Paulo, who moved here when the highway was first built. He has given up ranching and signed up to a government plan for sustainable forestry management, in the belief that it will be more profitable in the long term. Under the scheme, Paulo can selectively fell 10 per cent of the trees on his land: thus, he extracts the more valuable timber trees while the great biological intricacy of the rainforest remains substantially intact.

It was scary being in the jungle while trees were being felled, but Freddie was becoming increasingly fascinated. "So it can be done," he said, when we were back on the bikes. "People here have to make a living but Paulo showed us you don't have to cut the rainforest down to do it."

When the early Spanish explorer Francisco de Orellana made his epic journey down the Amazon River searching for "El Dorado" in the 1540s, there were an estimated five million indigenous people in the Amazon basin. Today, there are some 200,000 Indians left. We had hoped to spend time with the Tenharim tribe, first contacted in 1970, shortly before construction of the Trans-Amazonian Highway began. Today, the tribe operates a controversial and illegal toll on the highway, which crosses their land. Freddie and I paid our 10 reais (about £2.50) each to get through the gate but the tribal elders then wanted thousands of dollars if we were to stay the night and film with them.

The final 200km of our journey to Labrea were the worst. The midday heat became unbearable, the humidity intensified and the road deteriorated to a cratered quagmire. We had heard rumours that the highway is due to be paved. That would bring a huge influx of people, more gold mines, an increase in ranching and, inevitably, a spike in the rate of deforestation. On one particularly rough section of road on our last day, Freddie declared: "This road has a lot to answer for. My 'no man's land' is taking a battering." But it's a small price to pay to save the rainforest.

'Flintoff's Road to Nowhere' airs on Sky 1 HD on 4 and 11 April at 9pm. For more about Sky Rainforest Rescue: sky.com/rainforestrescue