By Neil Midgley, Ewan McGregor and Charley Boorman are off on a perilous bike trip for BBC2. They tell Neil Midgley about hunger, bickering and a near-death experience.

Ewan McGregor is reclining in a plush armchair in a suite at Claridge’s. It’s not just any suite: this one is so big that it has its own internal corridors, and enough space for an army of PR people to fuss about in anterooms. There’s an industrial-scale espresso machine, and McGregor is being served tea and biscuits by a flunky.

It’s a far cry from the journey that McGregor and his pal Charley Boorman are here to promote. Long Way Down, which starts on BBC2 on Sunday, charts their three-month motorbike ride from John O’Groats to Cape Town. It was a trip during which even the most basic luxuries were in short supply. “It’s things like showers,” says McGregor. “After camping day after day, the idea of having a shower becomes very appealing. But some of the hotels we stayed at were terrible too.”

Boorman chips in, relishing the horror of the journey from Ethiopia into Kenya. “We got to this hotel – and it was more like a knocking shop than anything else, with this boom-boom music blaring out,” he says. “The music stopped at 3.30am, and then at 4.00am the noise for morning prayers started. We thought, if only we’d just put our tents up somewhere…”

During the series, viewers will see McGregor and Boorman pitch their tents in a sandstorm in Libya, fall off their bikes and even come under machine gun attack from hostile bandits – though that is on a pre-departure training course near Daventry. In fact, preparation for setting off takes up the whole of the first episode. Harassed researchers plan routes and apply for no fewer than 90 visas to get McGregor, Boorman and their crew through 18 countries.

Boorman says he was never worried that rogues and ruffians would interrupt their travels. “We knew from Long Way Round that people are just people,” he says. “Having said that, you do get to a stage just before you go to Africa when you think, ‘What’s it really going to be like?’”

Long Way Round was the pair’s first televised motorbike ride, which, in 2004, took them from London to New York – travelling east. They had met (and discovered their shared love of motorbikes) in 1996 on the set of the film The Serpent’s Kiss, in which Boorman played McGregor’s secretary.

McGregor has subsequently made the Hollywood A-list playing the young Obi-Wan Kenobi in three Star Wars films. But being attacked with a lightsaber is, he says, child’s play compared to riding a motorbike through Africa.

“In Ethiopia there are these incredible mountains – staggering to look at, but you have to ride over them,” says McGregor. “And the roads are all very loose gravel, and it’s hairpin bends up the mountain and then hairpin bends down the other side. And very steep hairpin bends without bollards, so you could go over the edge and be 1,000ft in the air.”
Those Ethiopian mountains, says Boorman, gave him one of the trip’s biggest scares. “I was following Ewan,” he says, “and once you’ve committed on a hairpin bend it’s very difficult to change position. Ewan looked up, and there was this 28-wheeler truck coming down beside him. There was no way to go on the inside because the truck was already committed. So Ewan went across it and I was thinking, ‘He’s gone. That’s the last time I see Ewan.’ And then this truck goes past and Ewan pops out the other side. It was heart-stopping.”

Spending three months together under such intense conditions, says Boorman, made their friendship “a bit like a marriage” – with all the bickering that can entail. “Nearly every day we were packing up the tent and getting on the bike and riding another 300 or 400 miles, and sometimes you get very tired and hungry,” he says. “So you can become a bit niggly. Someone wants to do one thing, you want to do another.”

One objective for both McGregor and Boorman is to raise money for Unicef, and they stopped along the way in Uganda and Malawi to see the charity’s work with African children. Issues such as poverty and HIV are front and centre for their promotional interviews, though it becomes clear how long they’ve been away when another issue comes up: trust in television.

“What in television?” asks McGregor, plainly unaware of phone line frauds and royal strops that never were. “If people choose not to believe our series, I couldn’t care less – I know what we did, and that’s good enough for me. It would be so complicated to fake it, incredibly difficult to organise.”

He chuckles at the idea of Channel 4 hard man Bear Grylls staying covertly in posh hotels. “If there were hotels, we would stay in them,” McGregor says baldly. “If we were in a city, we stayed in Starwood hotels because they have a deal with Unicef – they mark up everyone’s bill by a dollar and all that money goes to Unicef. But what we don’t ever do is put our tents up, crawl in, then turn the camera off and go to a hotel.”

For McGregor, there would be no reason to fake the trip anyway. “It’s not a competition, we’re not trying to break any records,” he says. “We have got nothing to prove to anyone.”