Sport on TV: Trekkie boldly goes where no sane friends will follow him

When Ed Stafford hatched his plan to become the first person to trek the entire length of the Amazon and asked his friend Luke Collyer, an "expedition leader", to come along, he must have been excited. But after 100 days, Collyer decided to go home when it suddenly dawned on him that he wouldn't see his girlfriend for two and a half years. The fact that this eventuality had passed him by in the planning process suggests he's not the best expedition leader in the world. A trip down to Tesco sounds like the limit of his abilities.

Collyer had already admitted he found his other partner "completely unbearable" after about 10 minutes of the first part of Walking the Amazon (Discovery, Wednesday). Then he took off on his own to cross the Apurimac valley in Peru, the deepest gorge in the world, ignoring the paths chosen by local guides. It went horribly wrong.

"He put our lives at stake because of this emotional battle we're having," said Stafford. Collyer may have left him – and a whole bunch of worthy causes – in the lurch, but he checked out at the right time, just as they were about to enter the Red Zone, "battleground of the criminal drug trade" as the narrator told us.

Two thirds of the world's cocaine supplies come from here, which sounds like the sort of claim that could get a TV presenter in a lot of trouble with some powerful people. Next thing we know, he will be saying the coke brokers are lazy and feckless and flatulent, their food tastes like refried sick and their wives don't know the off-side rule.

Stafford, a former Army captain in Afghanistan, may have entertained a few thoughts of home himself as the locals gave him useful advice such as "You can't come through here, it's ridiculous. You'll get yourself killed". Then his guides ran away as well.

The problem, though, was not the drugs trade but the despised oil prospectors who swing periodically through the rainforest. People shouted "Death! Death!" from passing cars in the village of Cachingiri, and when Stafford called ahead to try and find some more guides, they said they would kill him too.

Then he was pelted with wet concrete – no doubt symbolically – and, mortified, he decided it might be better to try his luck on the other bank of the river – the drugs side. But on this bizarre journey into the heart of darkness, he was allowed safe passage there because the coca farmers had heard of his expedition.

Presumably a little Peruvian marching powder might have helped him on his way, too. He might have been hallucinating wildly when he said that some locals "came running up to me and said 'Hello Edward!'".

He found them eating a spider monkey, which disturbed him because they looked so human, but he was soon tucking in himself. And when he finally reached the flooded Amazon plain itself, after six days without meat, he gorged himself on a pregnant tortoise, putting aside its eggs for breakfast. Tortoise livers, singed tail of spider monkey – it sounded more Heston Blumenthal than Doctor Livingstone.

Finally there was a coming-of-age full-moon ritual called Pelizol, in which a young girl is released after being locked in a hut for two years. Boys run around with massive dildoes strapped to them. At least codpieces weren't on the menu too.