Ten years ago, aged 24, she set off on holiday to Africa with three other people and a Land Rover. Early on the two men in the party vanished into the night taking the Land Rover with them. Christina and her companion determinedly carried on, without food supplies or maps in a semi-desert area, firstly on foot but soon on horseback when two beasts were given them by passing road engineers.

"When you're thrown in at the deep end you either sink or swim," she told me, "but I found it was such a learning ground and I enjoy the learning. Everything changes once you lose a vehicle and you're down to your feet or the horses which we had. You can see the country in a different way because you can't carry everything ,that you need. You can't carry food supplies or much water so one becomes much more dependant on the land and the villages."

There is a globe trotting urge that runs in her family. Her grandparents spent 30 years in China before moving to Nigeria where Christina was born and where her parents lived for 20 years.

That first African jaunt seemed to awake the wanderlust within Christina and she was off again, "as soon as I'd done my spell at the Hospital Of Tropical Diseases and they'd put me on my feet", to see more of the Continent and make a 1,000 mile voyage on the rivers of the equatorial region in a dugout canoe.

In 1979 she set off for what was to become a two year trip to Papua New Guinea, some of it on foot, some on horseback (on a horse she called Horse) and four months of it in a canoe making the first complete navigation of the Sepik river.

Given a relief map of the globe, Christina goes for the lumpy parts. The PNG journey was made with a modicum of planning. Not surprising as it is one of the least well-charted regions on the planet and A-Z's are hardly two a penny.

"I found an encyclopaedia that said it had some of the wildest and most treacherous country in the world, that was part of the lure. I love remote places and mountains, I'm not frightened of that kind of thing. It seemed obvious that I should go and find out about it in the travelling.

"I didn't have any deadline, I just felt it would take as long as it took. I suppose I was setting off for between one and two years or possibly three. It entirely depended on the journey itself which I didn't plan out. I didn't even have a map of the country – I couldn't find anywhere to buy one.

"In a journey of two years you have time to learn as you go. It's like language. I'm on my own so there's no one to talk English to and I'm forced to learn a new language if I want to communicate."

The people of Papua New Guinea speak Pidgin – a quaint blend of Melanesian grammar with words of English, German, Malay, Portuguese and others. For example; 'Hoss brok-im leg. Im bugarap tru' – Horse broke leg. Him buggered up true.

"One begins to tune in a great deal to people's facial muscles when they speak and their tone of voice. Straight away you can tell if they're greeting you, threatening you or warning you about some problem up ahead.

"In the villages the women would make sure that I observed the local customs so that I didn't unwittingly cause offence. The men would always treat me like a man. They said I clearly wasn't just a woman – women didn't do what I was doing, their's didn't anyway. They gave me the status of 'honorary man'.

They say that fear is a man's best friend. But for an 'honorary man'?

"It didn't occur to me to be afraid. If you begin thinking that you ought to be afraid you start reacting differently to situations. You start seeing situations as threatening which needn't be. Or you can allow a situation to get out of control which could have been kept in control if perhaps you had shaken hands and said, pleased to meet you, what a wonderful country, I met your chief the other day, I'm from a village in England, which is your village?'.

"Of course, the moment you know their village that means there is no point in them attacking you at all because you can go straight to their headman. That kind of thing is frowned upon. In deep bush the moral code is much stricter than around towns.

"I'd learnt that there was no reason to be afraid and that people have no desire to harm you. Not being armed means that after a while your wits sharpen up. I've tried crazy ways of dealing with situations. Among the ones that don't work are 'the wrath of God', that something terrible will smite them – they don't seem to believe that. One quite good one is 'my husband, who is a large angry policeman and our five children are waiting for me in the next village' – that puts people off!"

I'll remember that next time I'm stuck behind someone in Tesco's. In her travels, Christina has spent time with cannibals. The popular imagination sees tourists being boiled in big black pots, with camera still slung around neck, searching through their phrase books for 'what's cooking?'.

"In New Guinea there are odd pockets of cannibals but it isn't anything that has any threat or anything to do with the traveller. It's something that's very superstitious. I spent a day with some cannibals but certainly didn't feel any threat. In Africa you can tell them because they sharpen their teeth to points. They say that human meat clings to the bone and you need sharp teeth to get it off."

And if she was invited to dine?

"I'd eat with them. Cannibalism is a very traditional celebration, it isn't just done for diet, it isn't a meal as such. It can be part of the baptism of a boy child or eaten in respect of a dead person (to let their spirit free). It has its reasons and it certainly isn't a question of throwing travellers into the pot and eating human flesh for supper."

Christina has sampled culinary delights such as crocodile's tail, rhino hump and elephants trunk ("nice if sliced thinly and eaten cold"), all considered delicacies in Africa. In Papua New Guinea the staple fare of kaukau (sweet potatoes) would sometimes be livened up by, among other things, maggots.

"When one's eaten maggots three or four times one isn't squeamish and if someone brings you a bowlful that they've spend the day gathering it would be impolite to go 'urgh!'. I have a caste-iron digestive system fortunately, I seem able to eat anything without ill effects although I had one bad day after eating a piece of rotten camel. I think that if you build up slowly by eating what's got just a few bacteria you then become immune to all but the most virulent form of nasties."

I ask my interviewee to roll her sleeve up. On her left shoulder she has the star-mark of the crocodile's forehead. It is impressive. I dropped my truth drug syringe! The mark was made in the PNG village of Kraimbit during the skin cutting ceremony which initiates boys into manhood. Their flesh is cut from their bellies, up their chests, over their shoulders then down their backs and legs.

"Once they've been through that, which is a blood ritual dedicated to the crocodile, they can meet every difficult situation knowing that they've had the courage to go through skin cutting. it represents a kind of triumph over the crocodile spirit.

"I'd spent a month in the region watching and helping the people get ready. There was a full week of sing-sing, drumming and dancing from dusk till dawn and everybody still feasting and celebrating. One starts to get a bit light-headed, the fear is much less that way. I didn't know it was coming, they sprang it on me. After they'd finished cutting the initiates they said 'are you ready to be marked by the crocodile?'. I said 'yes'.

"I've never regretted it, that mark is part of me. It was the highest honour they could give me."

During her adventures Christina keeps a diary and her account of the trip, in Papua New Guinea has recently been published in paperback by Picador (£3.50) – her previous volumes have included Travels With Fortune and An Explorer's Handbook.

For Christina these books help finance the next expedition and aid analysis of her experiences. For the reader they present enjoyably clear writing with the simple insights and lack of clutter that one won expect from someone who called her horse Horse.

"Writing is a separate adventure, I wouldn't like to travel in order to write about it because then I think the journey would be commercially motivated which would spoil for me. I only write about it because I have such a fun time and would be a shame if it wasn't written. I enjoy the writing as well. It's usually done when I travel around Europe or America – civilised areas because that's where can get paper!

"Writing can bring it all back very vividly. If I'm writing about a place where food was extremely short I'll keep dashing off to the kitchen to get something to eat. If I'm writing about going across the desert I'll need endless cups of water."