This exclusive extract is from Helen Clark's biography, Helen: Portrait of a Prime Minister, by her media adviser, Dr Brian Edwards.

Sex, booze and rock'n'roll were not for serious student Helen Clark. But, even at the age of 18, she was showing the willpower and intellect that would take her to New Zealand's top job.

It was not at all taken for granted in the Clark household that any of the girls would go to university. In Head and Shoulders (by Virginia Myers) Helen says that her parents were surprised that this was what she and Suzanne wanted to do. No one in the Clark family had ever been to university before, and primary school teaching was a more likely and more common career for intelligent young women of the time. But schoolteaching held little appeal for the 18-year-old, who wanted "something more stimulating than Training College".

And, increasingly, what Helen wanted, Helen got. Her refusal to play the organ or indeed attend church at all at Te Pahu was evidence of the emergence of a more determined and wilful personality than had previously been seen either by her parents or her teachers. George [her father] might have had occasion to think back to those "blue eyes staring at me" and his prediction that he "might have a certain amount of trouble".

No doubt some of this can be put down to that commonest cause of friction between parents and their children - teenage rebellion. But Helen had also had five years experience of life in New Zealand's largest city, a very different existence to that of her parents in the small rural community of Te Pahu. Changes were also occurring in her thinking and in her perception of the world around her.

She was becoming interested in politics, a different brand of politics to that of her parents. George and Margaret were staunch National Party supporters. They were farmers and the farming community was the backbone of the Party. Te Pahu was no different from anywhere else. "In our whole area," says Margaret, "you knew just the one or two who happened to be Social Credit or Labour. The rest were just en bloc National."

The unions were the farmers bete noir: "There was a strike in Horotiu one year and I reckon it cost me 20,000," George recalls. "You couldn't get your stock into the works, and they ate the grass others should have had, and so it went on and on down the system. That's why we were National Party."

On social and moral issues George and Margaret could also have been fairly described as conservative. Their oldest daughter, on the other hand, had begun in her final years at Epsom to see the world in a quite different light. Her ideas on the issues of the day - Vietnam, apartheid, nuclear weapons - were tending to the radical and left-wing, and she began to bring them home.

"Her ideas were diametrically opposed to ours in many ways," Margaret states. "I suppose she thought our ideas were ancient."

So Helen's visits home increasingly became occasions for arguments with her father, arguments which, Suzanne recalls, were heated and upsetting to the other members of the family: "It was awful. They used to argue terribly, mainly at the tea table. Helen would come home from boarding school and they would argue. She was very left-wing and my Dad, at that stage, was very right. And of course he loved an argument."