'SHE doesn't know I'm talking to you,' says Shuna, elder sister of Ffyona Campbell, who on Friday became the first woman to walk around the world. 'Ffyona is a powerful personality. Sometimes I feel she is taking me over.'

'Powerful' is one way of putting it. Others who have been close to Ffyona Campbell through her 19,000- mile journey - back-up drivers, television crews filming for the BBC2 series about her walk, journalists - have been, shall we say, less positive in their comments. 'Drama queen', 'incredibly difficult', 'basically a bitch', 'bananas', 'a stroppy, self- centred cow', even 'snarling wildebeest', are some of the milder names she has been called by disgruntled former colleagues and employees. But could anybody really be that ghastly? Or has she simply trodden on too many - mainly male - toes as she has marched round the globe? If anyone knows the real Ffyona, it should be Shuna, her only sister.

Shuna Campbell looks like Ffyona, but a darker-haired, more vulnerable version; at 29 she is the elder by two years. She is outgoing, works in the record business when not helping organise Ffyona's walk, and seems to enjoy rather than resent her sister's fame. 'I've only once told a man at a party who just wanted to talk about Ffyona to ---- off.'

The sisters were born in the West Country. Because their father, Colin, was a Royal Marine whose postings sometimes lasted as little as six months, they grew up on the move; their mother, Angela, was a full-time service wife, who struggled with the endless upheavals. Shuna and Ffyona went to 17 different schools, ranging from pukka convents to tough Scots comprehensives where they were teased for their officer-class accents.

The forces that were to help make Ffyona a world-walker were shaping her future before she was even born. 'My parents had a list of names ready before she arrived. They were all boys' names. I had no idea of this until Ffyona said to me not long ago, 'Don't you understand Nick?' - she calls me Nick - 'Daddy wanted a boy.' '

When Ffyona was 10, Shuna, then 12, suffered a brain haemorrhage. 'That was when the trouble began. Ffyona was left in the background and had to soldier on alone. She became the elder sister, the one in charge.

'I couldn't walk, I was so thin I once got trapped in the loo seat. She had to look after me. She used to tell me wonderful stories, which I can never forget. I had my head partly shaved, I had to wear a little hat and people would make fun of me. But every breaktime and lunchtime at school, she kept them away from me.'

Their parents, however, still treated Ffyona as the younger sister she was. Though fully recovered Shuna was, at that stage, slow to mature, quiet and hardworking, unlike Ffyona. 'When Ffyona wanted to go to discos, our parents said you can't because Shuna hasn't done that yet. Once I heard Fi and Mummy having a huge row about it. She still has this thing about 'eldest perks'. Most people grow out of it but she hasn't. All that anger, all that resentment is still with her. She keeps it all bottled up inside and can't get rid of it.'

After the illness, Shuna continued to attract all the attention. Their father was now working as a pilot. 'When she was 14, Ffyona started to take flying lessons and plastered her bedroom wall with plane pictures to get attention. Daddy would help me with my homework and say good night to me but he'd sometimes forget to say goodnight to Ffyona. He was working really hard and maybe these were freak incidents, but Ffyona and I talk about it a lot,' Shuna says.

'We discovered when we talked about this recently that in fact she had got better grades than me at school. My parents had just forgotten that. It was all, 'Look at what Shuna has been through and now she's going to the University of St Andrews'.'

There is a talent for self-dramatisation in both sisters. Shuna explains cheerfully: 'We're both show-offs. At school we both used to take on different personalities everywhere we went. If you admired a sporty person at the previous school, you would make out you were really sporty at the next one. Next time, you would be studious. We used to win prizes for acting.'

The experience of relentlessly changing schools has made Shuna confident and quick to make friends. But Ffyona, travelling on and off for 11 years, has only a handful of ex-boyfriends and others to whom she is close.

The sisters support one another. If Ffyona's home is anywhere, it is Shuna's London flat. Shuna organised the logistical support for much of her sister's trans-Africa walk and she lost two jobs over the amount of work she was devoting to Ffyona's travels. The relationship strikes outsiders as unusually intense - not least Shuna's ex-husband. He cited Ffyona's 'continual presence in the matrimonial home and her influence' when resisting Shuna's application for a divorce.

Shuna says this was nonsense. 'She phoned and came round a lot, but she only stayed once, for a few weeks. I knew that a successful marriage depended on spending time together as a couple and building a home. But he had lied about his age, about having a first-class degree from Oxford and that was just the start of it all.' It was Ffyona who checked with the university and found it had never heard of him. When Ffyona rang up and told Shuna, Shuna at once believed her sister, not her husband.

Shuna, who has bounced back resiliently from her painful divorce, worries about her sister. 'Ffyona is spending too much time on her own, focusing too much on one thing and following thoughts off all over the place.' Shuna used to torture herself with obsessive little rituals when she suffered from anorexia as a teenager - 'like, just how awful will I feel if I eat this Ryvita'. Shuna feels the mind games Ffyona plays to haul herself across the endless miles are destructive. 'She used to decorate a whole house in her mind in a day's walk. Now it's just choosing the colour of one lampshade. You lose sight of where you are going like that. She got to feel almost persecuted by the film crew, feeling that they were out to get her. They were, but Ffyona built it all beyond that in her mind.'

The sisters have a pact for the future. 'We used to read the Famous Five books and we thought that if only we had cousins, we wouldn't have to make new friends all the time and leave them. We decided we would one day live quite close to each other in white cottages with roses round the door. Her children would be gypsy kids, with no shoes and long robes and long blonde hair, and mine would be more conventional. But they would all be cousins.'

(Photograph omitted)