It is, perhaps, his most convincing performance yet. In 2004 Ewan McGregor took the lead role in a grand production called Long Way Round, where he played the part of a benevolent actor-adventurer circumnavigating the world via Unicef projects on a shiny new motorbike.

Starting in London, finishing in New York, with only his thoughts, his best friend Charley Boorman and a TV crew for company, Scotland’s spikiest leading man chewed up three continents in three months. There were flat tyres, there were tantrums, but damn it they got there.

Long Way Round – which was inspired by Ted Simon’s 1970s motorbike epic, Jupiter’s Travels – captured the hearts and wallets of the nation who, as well as keeping the pair’s travel-

ogue in the Sunday Times best-sellers’ list for weeks, watched the accompanying television and web serialisations in droves.

This year, hoping to disprove the old wisdom that you can have too much of a good thing, McGregor, 36, and Boorman, 41, hit the road again in Long Way Down – a 15,000-mile journey from John o’ Groats to Cape Town.

The actors completed Long Way Down, a trip through 18 countries in three months, in September. For McGregor and Boorman – two motorbike obsessives who bonded over the Scotsman’s purring Moto Guzzi on the set of The Serpent’s Kiss 11 years ago and who are now godfathers to each other’s children – it was another “once in a lifetime” experience.

It was also a trip that provided, for McGregor, some welcome respite from Britain’s “nanny state”. Indeed, he says that if “anything were to drive me out of the country, it would be that . . . the CCTV cameras everywhere, the congestion charge”.

Fine sentiments – but as he and Boorman plug the forthcoming Long Way Down multi-media avalanche from their suite in Claridge’s, one has to wonder whether having the cameramen along for the ride rather ruins the free-spirited, sandflies-in-the-visor escapism of it all?

“Not at all,” says McGregor.

“Because, to us, the thrill of adventure and travel to places where you would not normally go, is so fulfilling. So for other people to see that on television is going to be incredibly interesting. A lot of popular television is about exactly the opposite of what we did. It’s just people being locked in a room for three months and us watching them go insane. Our trip is about seeing the world.”

Travelling through countries such as Libya, Sudan and Ugan-da, they certainly saw Africa, albeit at a variety of shutter speeds. They tore through much of the continent, riding as much as 400 miles a day. But when they stopped and looked, Africa threw up some surprises – not least a meeting with Paul Kagame, president of Rwanda.

“It was very odd,” says McGregor. “We’d stopped in Kigali at this coffee shop and we got chatting to a woman who turned out to be the Rwandan minister for tourism. We told her what we were up to and she invited us to a wedding that night.

“We didn’t have any smart clothes so we turned up in jeans and T-shirts and caught a few frowns from the guests, but we did get to meet the president. He was a cool guy – very quiet – and we were invited to his house for a meeting the next day.

“So we thought, we’ve got to buy something smart, and we went out to buy clothes from the market . . . But when we turned up, he came to the door in jeans and T-shirt. We had a laugh about it, then we had an hour together. He told us his plans for the future of the country.

“To me, it seemed like one of the most forward-thinking places we visited. Of course your mind is full of the horrific events of 13 years ago, but in reality the country has moved on. The president has even instituted this thing where on the last Saturday of every month everyone does something for the community. It’s been a huge success.”

The Kagame meeting was a rare moment of hobnobbing in what was otherwise a rough and ready experience. The actors, who were raising money for Unicef, Riders for Health and the Children’s Hospice Association Scotland, visited charity projects along the way. Two visits, one to a clinic in Kenya and one to northern Namibia, provided a bleak contrast.

From one clinic in Kenya, supported by Riders for Health, a 45-mile area was serviced by trained motorcyclists providing medical provisions and supplies to villages. By using motorbikes, not only had the number of people receiving prescriptions and mosquito nets risen, but understanding of diseases such as Aids and dysentery had grown.

In the areas the actors visited in northern Namibia, no such scheme existed. Aids sufferers were being treated with traditional medicines and as outcasts. Although people would walk 20 miles to find food, they would not bring antiretroviral drugs back to the village. It was, says McGregor, “desperate to see”.

Most of the pair’s memories are sunnier than this. Boorman relates mostly “very positive” experiences and McGregor recalls feeling “safe the entire time, and we camped everywhere”. The route they travelled, meanwhile, was a “feast for the mind”, although, says McGregor, a feast with some nasty courses.

The pair came across some “pretty gnarly roadkill”, the high-lights of which were months-old rotting camels sprawled across the road in the Libyan desert, and a donkey that had exploded in a car crash just outside Addis Ababa. And the wildlife, it seems, was pretty keen to see some exotic roadkill of its own.

“We were doing about 80mph on this left-hander in Namibia,” recalls McGregor. “All of a sudden I saw this huge kudu [antelope]. As we came towards it, I couldn’t really change direction, and this thought came into my head, ‘You can either walk left and it’s all f****** over. Or you can turn right and everybody’s laughing’.”

Happily for McGregor, Boorman and the kudu, it went right. But as much as the incident now provides some boyish banter, it is a story you might not enjoy so much if you were related to, or indeed living with, either man. Both McGregor and Boorman are married with two daughters. They have now succeeded twice in being written the ultimate free pass from their wives. How?

“Hang on,” says McGregor, eyes burning. “Your question implies that we’re trying to get away from our wives.” No, I explain – suddenly remembering that McGregor has form when the rock-solid nature of his private life is queried – it implies that you spend a long time apart from your families.

“Listen,” he says, “we go with the full blessing and understanding of our families. It’s not something we have to have a ruck about. We discussed [Long Way Round] as the evolution of trips that Charley and I had already taken together, and after the success of that, and how much we got out of it personally, it was nice to do another one.”

Boorman plays the peacemaker – a role he has, one suspects, taken before – and gently explains that McGregor’s wife, Eve, came out and rode a section of their latest journey with them. “It was lovely,” he says. “She got a very good sense of what it’s like for us when we’re doing these trips.”

And what are the trips like? Do McGregor and Boorman argue? Do they share a tent?

“Not this time,” says McGregor, brightening up. “No, we decided to have separate tents. We’re up and down. It’s like any relationship. It can be tough living with someone 24 hours a day for three months. It’s intense. We don’t get that time alone with our partners. So it’s a challenge – you’re challenged physically and mentally – but it’s an awful lot of fun.”

No doubt it’s fun and this sense of fun makes passable television. But whether these two superannuated gap-year kids have achieved anything is moot. They argue that they bring “exposure” (and cash) to some worthy causes. Fair enough – but there’s something in the manner of their doing so that bridles.

It takes Boorman to cut to the nub of the matter. “What we really wanted,” he says, “is for us to be 70 or 80 years old and to be able to look at the book or the programmes and have a bit of a giggle about what went on.”

In which case, job done.

Long Way Down starts on BBC2 tonight at 9pm

Explore UK News

• Crime News

• Education News

• Health News

• Science News

• Scotland News

Times Recommends

• Third of Muslim students back killings
• Curfew tames feral yobs of Cornwall
• £3,000-a-month drug free abroad