Deep in the African bush Sarah Finlay and Henry Douglas, two Scottish conservation workers, were in conversation about the future of Kenyan rhinos when they heard the sound of motorbike engines. They looked up as the bikes approached, trailing blood-red dust, and when the riders dismounted heard the unmistakable burr of home.

“This was the last place I expected to hear a Scottish accent,” says Finlay, “never mind bump into a Hollywood movie star. We couldn’t believe it when we realised who it was.”

Ewan McGregor and Charley Boorman, last seen on these pages disappearing eastward in 2004 aboard two BMW off-road motorbikes, have swapped the snow of Siberia for the sands of the African savannah. The pair are en route to Cape Town after setting off from John o’ Groats in May, and are now crossing Malawi, more than halfway through a trip that takes in 20 countries, including Libya, Ethiopia, Sudan and Rwanda.

The journey hasn’t been easy. The pair have had to contend with sandstorms that reduced visibility to a few feet, border crossings guarded by fidgety soldiers, damaged bikes and an indigenous population whose favoured fashion accessory is an AK47 assault rifle. It is about as far from the glamour of Hollywood and the pampered life of film stars as you can get, but according to McGregor he wouldn’t have it any other way.

“It’s been incredible,” he says via satellite phone during a break in the riding. “It feels like a real privilege. You just don’t see some of the remote villages that we have ridden through unless you are an aid worker – these are real mud-hut, thatched-roof villages, not really places that tourists get to go. We have had our ups and downs, though, as you would expect.”

Named by them the Long Way Down (as opposed to the Long Way Round, their previous east to west trip that saw them ride from Britain through eastern Europe and via Alaska to New York) this latest trip will see the pair travel 15,000 miles over some of the most inhospitable terrain and lawless countries on earth.

The two riders are accompanied by a cameraman, Claudio Van Planta, on a bike, while two Nissan pickups travel a few hours behind them and carry a five-man team made up of a medic, security adviser and camera crew. Each rider also has a camera fitted to his helmet to capture more intimate moments of life on the road.

McGregor and Boorman first met on the set of Philippe Rousselot’s film The Serpent’s Kiss in 1996. Charley is the son of the director John Boorman, starring in many of his father’s films such as Deliverance and Hope and Glory. But it’s their shared love of bikes that has cemented their friendship: McGregor has been riding bikes since he was a teenager and Boorman recently competed in the Paris-Dakar race.

The first trip in 2004 was originally billed as a chance for them to escape the luxuries and distractions of modern life as well as the celebrity gossip columns. However, it turned out only to feed people’s fascination. Far from being a non-profit-making call of the wild, the DVD and the book of Long Way Round earned them a reported £3.5m, while the television rights went on to sell in 40 countries including the United States, Australia and Japan.

Still, there is no doubting that both McGregor and Boorman are enjoying the isolation and anonymity their ride is affording them, up to a point: on passing through Tunisia – a country used as a location for the Star Wars films that McGregor starred in as Obi-Wan Kenobi – he was a little put out that nobody recognised him.

Ewan McGregor

A trip like this opens up a certain part of your brain. After the Long Way Round someone warned us that it would be an addictive thing to do and that has been the case. It’s also about seeing a different way of life to ours.

Travelling on a bike makes a difference, too: you feel more exposed to the elements – if it rains you get wet, if you go through an area where there’s a burning tyre you smell burning rubber. You feel part of it all. And of course you can fall off and hurt yourself.

Some of the riding has been hard. There was a period in Sudan where I had a rough day in deep sand and I have never really cracked how to ride in it. I have fallen off a lot.

What happens when you get into deep sand is the front end starts wobbling and you feel like you are losing all balance. You tend to let the throttle off so that you slow down, and tighten up your arms, which immediately puts all the weight on the front wheel, which means that you will just fall off. You have to train yourself to do the opposite: keep the power steady to push it through the sand but put your weight slightly further back. I am getting better at it.

We have also faced the complexity of Africa: some of the places you pass through are beautiful, like something out of an Indiana Jones film or the National Geographic. In Ethiopia we were riding through villages you fantasise about: mud huts and straw roofs, little kids running around in raggedy clothes and snotty noses and just so friendly. But you know also they have no sanitation or medication or access to clean water.

You’re faced with this contradiction of the fact you are having a great time, you really have a sense of exploration and adventure and at the same time you are seeing something that makes you sad.

People do have guns here, but it doesn’t seem to worry me any more. Someone said that in eastern Europe everyone carried a gun but you didn’t see it, whereas here everyone carries a gun but you do see it. That’s true, but I think here they are more of a fashion accessory than anything else. I hope.

The only time I have been worried is when we were doing this section in Egypt and going through a lot of road blocks. There were these guys in long shirts and they had these long rifles. They didn’t look like policemen and yet they were operating these road blocks.

I don’t really miss anything about home. You sometimes miss your families and friends and everyone has their off days, but it tends to hit you when you are not doing anything and we have been riding pretty solidly – we have set ourselves a target of reaching Cape Town within three months. There’s certainly no material thing that I have at home that I miss.

And that is another great thing about being here: you have only what you can carry and there is something liberating about just having what you need, on your bike. A tent, a roll mat, water, a little bit of food, a bit of petrol in your tank and a vague idea of where you are going and that’s all you need. There is something beautiful about that.

Charley Boorman

The worst day so far was in Libya. We were camping on the beach and all of a sudden the wind changed and this huge sandstorm kicked up.

The tents were being blown away and we were all just trying to bash the tent pegs back down with everyone holding on desperately for the morning.

In the morning the wind had died but was still bad and then we had to get on our bikes for a big ride to the Ethiopian border. I remember that was about 15 hours in this massive sandstorm. Sometimes Ewan was about 15 yards ahead and I couldn’t see him. He said it was like someone was pouring millions of tons of brown sugar in front of you. We ended up at Tubruk at 1am shattered.

But the riding has been amazing, despite the falling off. One of the great things about biking is that everything changes slowly. It is not like you have just been dropped off in an aeroplane in the middle of this unfamiliar place. So you see the people’s faces changing slowly and the countryside and the atmosphere of each place and it all follows logically.

For me Ethiopia has been the biggest surprise. There aren’t many cars because everybody walks with their stuff, so you have everything on the road: camels and goats and cows and all the people carrying everything. In Britain you see these things in magazines about the best roads to ride and I just think that Ethiopia eclipses everything.

The other big surprise has been going through so many countries where people at home automatically think it’s dangerous: so Sudan is a dodgy place, Libya “oh that’s dodgy”, but if you go to these countries they are fabulous. I know that there are problems in Darfur but where we were up in the north, and following down the Nile, it was great.

We have seen the problems, too. In northern Uganda where the LRA [Lord’s Resistance Army] have been fighting we visited a Unicef project that was looking after former child soldiers and spoke to a boy and girl who were about 10 years old. They had been raped, forced to kill people . . . it was unimaginable.

You have a lot of time to think about things here because a lot of the time you are in your own helmet doing your own thing. Your mind wanders and you think about all sorts of things that you haven’t thought about for a long time. I lost my sister to cancer about 11 years ago and at home you don’t have time to think about things but here you have all day. My sister pops into my mind every so often so I have a nice think about her. It’s a great therapeutic thing.

Travelling with Ewan has been great. We are still speaking to one another – through a mediator – although you have ups and downs when you travel like this. You can feel great in the morning and not so great in the afternoon. If one of us is feeling low or needs time alone the other one knows it.

We know how lucky we are. Apart from anything else it’s great fun to be able to see all of this around us every day, to be with your mate and to be riding bikes through Africa.

— Follow the team’s progress at www.longwaydown.com

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