Three of the Harrisons’ children had such profound dyslexia, they were told they would never learn to read or write. In 1970, when their eldest daughter, Wanda, then five, began to hide rather than go to school, Iris decided to keep her at home. To escape the authorities, the family fled to a remote Scottish island, to a hut with no running water. The nearest shop was a boat ride away. Iris recalls Wanda learning to read from old copies of Exchange & Mart. “In the end we decided we couldn’t keep running. We came back, hoping we’d be forgotten.” They weren’t. They were threatened with legal action and told that the children, including six-month-old Newall, would be taken into care.

“The children were so afraid, I barely left them,” Iris recalls. “The LEA [local education authority] were like the Gestapo. I remember once having to go out to get petrol and telling my eldest son, Grant, that if the authorities arrived, he should load his air rifle and aim at their feet.” The Harrisons instructed a lawyer and bought a flock of geese to keep the LEA inspectors away, while they and a handful of supporters fought their way through the courts for the right to educate their children autonomously at home.

Autonomous learning is child- rather than teacher-led. Parents become facilitators, providing resources and assistance, allowing children to follow their own interests. “We played games, we researched every question they asked,” says Iris. “We didn’t have a TV. It was a talking, living education.” Iris’s diary around this time reads: “AJ’s violin lesson went on all day today. Newall worked on his model farm, working out the grazing required per animal.

He then calculated the cereal crop requirement, hay for fodder and allowed an amount for sale. He and Grant have been researching ancient weapons using the World of Knowledge. They made a replica of a Roman weapon and set up a battle in miniature…”

Iris felt “the deepest certainty” that they were doing the right thing. Her husband had spent his school days truanting in museums, remembering everything he saw. “I trained purely to take exams and immediately forgot everything,” says Iris. “It was obvious that he was the one who was truly educated.” Today their children, now in their thirties, still love learning, and continue to study – though not, says Iris, to take exams. AJ trained in alternative medicine, Wanda has worked teaching new skills to young people, and Grant runs a workshop making ironwork with Newall, who also renovates classic cars.

The 1944 Education Act states that the parent of every school-age child should ensure he receives full-time education suitable to his age and ability, “either by regular attendance at school or otherwise”. It is the word “otherwise” that provided the Harrisons’ legal loophole and opened up home education as an option for all.

In 1977, so few families were educating their children at home that nobody bothered to count them. By 1978, Education Otherwise (EO), the support group Iris Harrison co-founded, had 400 member families. The figure is now 4,183, and EO’s helpline receives 700 calls a month.

The Department for Education and Skills estimates that up to 150,000 children in Britain may be home-educated. The exact figure is impossible to calculate since, if their children have never been registered at a school, parents have no legal duty to inform the authorities. But we do know that profile of the modern home educator has changed. Many parents who opted out of mainstream education in the 1970s were exploring an alternative lifestyle. Nowadays, large class sizes, bullying, failing to get a child into a school of their choice and the relentless pressure of exams have led many parents who wouldn’t consider themselves remotely radical to remove their children from the system.

When Rowan Hillier, 13, didn’t get into her first or second choice of secondary school near Tunbridge Wells, her parents ignored the third, “the kind of school where the kids beat the teachers up”. Rowan has been learning at home for nearly two years. “I was certain I could do better,” says her mother, Jane Brenan. One hour’s tutoring a week in maths, science and French has kept Rowan on top of the national curriculum.

“At first I found being together all day oppressive,” says Jane. But Rowan quickly saw the advantages: “Once I’d done my work, I could play my guitar all afternoon.” She kept in touch with her old schoolfriends and fell in with a local group of “home eds”. Her only problem was distinguishing their tribe. “In school you go, ‘Okay… pikey, goth, chav and emo.’ With home eds you can’t tell.” A place has become available at a local school for September and Rowan has decided to take it. “The past two years have been a good experience,” says Jane. “I’m all for structured learning, but my experience with my eldest daughter, now 21, made me realise that children have very little choice over how and what they learn. Holly did very well, but she worked out that by the time she’d finished her A-levels, she’d taken 160 exams.”

An apparent prickliness among home educators makes collecting information difficult. When Mike Fortune-Wood of the Centre for Personalised Education Trust began researching home-based education in 2002, only 263 families replied to a widely distributed questionnaire. While home educators meet socially and to share skills, more formal networks seem to be hampered by differences between home educators themselves. A minority use national-curriculum textbooks and invent their own timetables; others are free to choose what and when to learn. This may involve long hours watching MTV as if in a coma. In HE parlance, this is called detoxifying from school. Leslie Safran-Barson runs the Otherwise Club in London, a community centre for home educators. She recalls her son Louis, who this year gained a first in philosophy from King’s College, London, lying on the floor staring at the ceiling for hours, and spending whole days superglued to his PlayStation. Clearly, home educators need to have nerves of steel. Safran-Barson, who rejected school for imposing “too much structure, too soon” believes that laziness is a reaction to not being listened to, and that eventually even the most disaffected child will get off the sofa and discover a passion for something, because children are hard-wired to learn. When Louis declared an interest in science, she found a medical student who spent a few hours a week talking human biology. History was studied by getting a group of local children together and researching different periods, finishing with a play they wrote and performed themselves.

Christopher Ford’s mother, Helen, admits to panicking when he could barely write at 11: “He went to school for one term, hated the narrowness, left and we didn’t look back.” Chris took his first GCSE when he was 13, started a biology degree at Sheffield University at 17 and took his finals this year. He is predicted to get a 2:1 or a first and is applying to do a PhD at Edinburgh. Ruth Charles, 21, is taking a degree in community and youth work at Durham University. She and her sister Ann, 19, have never been to school. “My parents just didn’t think any of the schools locally were good enough,” says Ruth. “Mum thought, ‘I’ve already taught them to walk and talk. Why can’t I teach them the rest?’”