Ewan forced to take doctor with him on dangerous journey into bandit country

At the insistence of his insurers, the 36-year-old star is to be accompanied by Dr Dai Jones, a trained paramedic who has worked in war zones worldwide.

On their three-month adventure, McGregor and his friend Charley Boorman, 40, will pass through seven countries which the Foreign and Commonwealth Office advises Britons not to visit.

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Ewan McGregor's journey wil take him through seven different 'no-go' countries

Dr Jones, who developed his skills in Afghanistan and Iraq, will travel with the BBC film crew shadowing the pair on their journey from Scotland to South Africa.

The 15,000-mile trip through 20 countries has been dubbed the Long Way Down. It follows McGregor and Boorman's 2004 trek from London to New York through Asia, which was made into a documentary called The Long Way Round.

But while they will pass through lawless areas ruled by armed tribesmen, Dr Jones, who has experience in treating everything from scorpion stings to gunshot wounds, thinks Africa's roads pose the main danger.

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Heavilty armed militia and bandits will be a major hazard

He said: "We're going through some dodgy areas. There are lot of risks to health, but I think the biggest concern is road traffic accidents.

"Long Way Down will be very different to the last trip.

"Last time they were riding mostly through unpopulated areas, whereas most places in Africa will be pretty busy. We have to consider injuries plus security, which is why the support crew will stay closer to the guys than before, so we can be there quickly if they have any dramas."

Welshman Dr Jones added: "To be honest, if we can avoid the badness in the worst areas, the biggest risk is going to be the guys falling off the bikes and hurting themselves, or the 4x4 support vehicles rolling, like one did in Long Way Round.

That's why I've trained them in helmet removal, spinal protection, that kind of thing."

The celebrity bikers, who set off from John O'Groats a week ago, will travel through Europe in the first stages of their trip.

Yesterday, they loaded their motorbikes on to the Channel Tunnel Eurostar shuttle at Dover and intend heading through France and Italy.

They will catch a ferry to Tunisia and travel through Libya, Egypt, Sudan, Ethiopia, Kenya, Uganda, Burundi, Congo, Rwanda, Tanzania, Malawi, Zambia, Mozambique, Botswana and Namibia before arriving in Cape Town.

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The journey will take in seven countries on the Foreign Office's no-go list

The mammoth trek will finish at the southernmost point of South Africa, Cape Agulhas, where the Indian Ocean meets the Atlantic.

Many countries on the route are listed by the Foreign and Commonwealth Office as high risk areas, but seven – Burundi, Democratic Republic of the Congo, Ethiopia, Sudan, Uganda, Rwanda and Zambia are specially singled out as "Countries the FCO advises against all but essential travel to".

Many are plagued by banditry and lawlessness, while ruthless armed militias are also active in some remote regions.

In addition, large tracts of country are seeded with landmines, while HIV/Aids and other killer diseases are endemic.

Organisers have revealed that McGregor and Boorman trained at a bush survival school and had lessons in self-defence from former Special Forces soldiers before they set off.

They have also had vaccinations for a range of illnesses including hepatitis A, polio, rabies, yellow fever, typhoid, tetanus and meningitis.

In The Long Way Round three years ago, which was made into a television series and successful book, the friends rode from London to New York on a 19,000 mile epic journey through 12 countries.

These included the Czech Republic, Ukraine, Russia, Kazakhstan, Mongolia, Siberia and Canada.

Along the way they had to negotiate roads that were little more than rough tracks, cross numerous swollen rivers and deal with obstructive officials at border crossings.

This time McGregor, a UNICEF Goodwill Ambassador, plans to visit the organisation's projects in impoverished Ethiopia, Uganda, Malawi and Zambia.

Both riders made light of the risks before setting off from Caithness. McGregor joked: "I've really got to speak to my wife, otherwise she might not let me go.

"I haven't told her that we are leaving yet. I just said I went out to get some milk."

Boorman added: "There's a huge amount we're really looking forward to. The pyramids, obviously. The Nile, and Ethiopia, which many people say is the birthplace of mankind, so that should be amazing.

"Then there's the mighty Okavango Delta wetlands, the bushmen in Namibia, I could go on for ever.

"Of course, there's a few places we're a bit nervous about, such as Sudan. But going down the east side makes more sense than going west, where there are probably more problems."

The pair will be riding BMW R1200GS motorbikes, which have been specially kitted out with GPS, crash bars and walkie talkies.