The guru with a gift for brainwashing

Thierry Tilly looks like a geography teacher or a chartered accountant, or a French version of Bill Gates. He claims, variously, to be a Nato "master-spy", a confidant of presidents and prime ministers, a financial genius, a 21st-century representative of an ancient, secret order descended from the Knights Templar and a man with superhuman powers sworn to fight the forces of evil.

He is now in a French prison, refusing to answer questions on possible charges of kidnap, brutality and torture. Seven or eight of his followers, from three generations of a French aristocratic family, are living in Oxford, Tilly's base for the past nine years. One of them, formerly a gynaecologist, is working as a gardener. Others have jobs in fast-food restaurants. Until 2006, 11 members of the family had spent five years barricaded in their château at Monflanquin, 100 miles east of Bordeaux.

Their relatives say they remain under the spell of a lurid fantasy, which might have been torn from the pages of a Dan Brown thriller. They have been convinced by Tilly that their family – the De Védrines, part of the Protestant nobility of south-west France for 300 years – has been chosen to struggle against supreme evil by an ancient order called L'Equilibre du Monde (The Balance of the World). Lawyers and relatives say they refuse to accept that they have been duped and fleeced of the family fortune of up to €5m (£4.5m) by an unscrupulous, possibly deranged but mysteriously effective con-man.

Angry landlords in Oxford, owed tens of thousands of pounds by Tilly and his followers, say the De Védrines, aged from 96 to 24, are not necessarily all victims. Some members of the clan, they say, have become Tilly's willing accomplices.

Dotty sect or elaborate fraud? Either way, since the arrest of Thierry Tilly, 44, in Switzerland last month, relatives in France are desperately worried. They fear that the "Oxford Eight" (or perhaps seven) may be so deeply under Tilly's spell that they could fall victim to a mass suicide pact. They are angry that British authorities have refused to treat the Tilly affair seriously for more than eight months.

Jean Marchand, 62, a former financial journalist, has run an almost single-handed crusade against Tilly for eight years. The Oxford Eight include his former wife, Ghislaine de Vedrines, 55, and his two children, Guillemette, 32, and François, 30. In September 2001, they abruptly severed all ties with M. Marchand, whom they declared to be an "agent of evil". His daughter, Guillemette, then 24, abandoned her husband after only four months of marriage. Neither husband nor father has seen her since.

M. Marchand's wife and children barricaded themselves into the family mansion in France with Ghislaine's elderly mother, also called Guillemette. They were joined by Ghislaine's two highly educated and successful brothers, Philippe, then 56, and Charles- Henri, 53, Charles-Henri's wife Christine, 51, and their three children, Guillaume, 24, Amaury, 21 and Diane, 16. The transfer of the family to Oxford began in 2006.

"I still cannot explain Tilly's hold on my family. It is a kind of mental kidnapping," M. Marchand said. "He does not even have to be physically present to control them. Almost from the beginning, he has issued most of his orders by telephone or by email and they have always obeyed him."

For years, the French judicial authorities refused to intervene, despite a police investigation which showed that the family fortune, in cash, furniture, paintings, jewelry and property, was being systematically liquidated and transferred to accounts controlled by Tilly. In March this year, Charles-Henri's wife, Christine, fled the group in Oxford and returned to France.

She told French police she had been tortured, physically and mentally, beaten and kept for days in darkened rooms. The ill-treatment, she said, was supposed to dredge from deep in her unconscious the whereabouts of a lost treasure of the Knights Templar, the powerful, shadowy, medieval order of chivalry suppressed by the French monarchy in 1307.

The French authorities issued a European arrest warrant. But. despite several requests by a French investigating magistrate, the British judicial authorities refused to honour the warrant for technical reasons. Tilly was finally arrested aboard an aircraft at Zurich airport on 21 October and extradited to France.

"You might think, or hope, that, with Tilly under arrest, the spell would be broken and they would return, painfully, to reality," M. Marchand told The Independent in his Paris suburban home, still crowded with portraits of his lost family. "But no, it seems not. They are just as much under his spell as they were before.

"I keep thinking of the Temple du Soleil and Jim Jones' followers in Guyana [sects which entered mass suicide pacts in 1994 and 1978]. What kind of instructions has Tilly given them? Time may be short. The authorities in France have started to take this affair seriously but in Britain we are still being ignored."

A few days ago, M. Marchand and his lawyer, an expert criminal psychologist, and other helpers visited Oxford and tried to speak to his relatives, now living in guest-houses, expelled from large houses after they failed to pay rent. The attempt led to violent verbal clashes, photographed and filmed by French journalists. M. Marchand tried to accost his son, François, on the street, leading to another shouting match. Oxford police told M. Marchand there was nothing they could do.

"I love Britain. I have a great admiration for Britain," M. Mar-chand said. "But the attitude of the UK judicial system in this affair has been unhelpful and obstructive since the beginning. Tilly is a convicted fraudster, with other legal problems in Britain and France. He is being sued, many times over, by ex-landlords in Oxford. The French investigating magistrate has asked for the right simply to interview the members of the De Védrines family still in Oxford. He has been systematically refused."

M. Marchand is especially worried about his daughter, Guillemette, who has not been seen in public for months. In theory, she is still in Oxford but Mr Marchand fears she has been taken elsewhere; or that something worse may have happened to her.

Philippe de Védrines, a former oil executive, now 71, was the first family member to "escape" from Tilly, with his wife Brigitte, 61, in 2008. Much of the French police information on Tilly's methods and far-fetched claims comes from Philippe, now living in Normandy. He refuses to bring a legal action or talk to the press.

The second breakthrough came in March this year. Christine de Védrines, 59, the wife of the former gynaecologist, Charles-Henri, was persuaded to flee from Tilly by a Frenchman, living in Oxford, for whom she worked as a cook. Robert Pouget was born in Paris and educated in Britain. He came back to England after his French military service and started a business in Oxford selling fresh produce. Mr Pouget said: "After more than a year of working for me, we sat discussing things one night after hours and she just came out with all of it, the whole story.

"She had been incarcerated of her own volition with these people. They had told her she was the direct descendant of people who knew where treasure, handed down from generation to generation, had been hidden by the Knights Templar as a fund to help French aristocrats if they got into trouble: except, she couldn't remember where it was hidden or how to get it. She said she was taken from bank to bank in Brussels to try to find it but she just couldn't remember. I told her that was because she had never known. She was told a lie."

Mr Pouget arranged for Christine to call a cousin in France, who came to collect her within two days. "Christine was a very sweet, nice woman. She was good-natured and kind. When she came to work with normal people, little by little I think, the realisation dawned that it was all an illusion."

Andrew Scully, 48, also rues the day he ever met Thierry Tilly and the De Védrines. Since renting two houses in Cornwallis Road, Oxford, to Tilly and Guillaume, in 2006 he has been involved in 19 court cases, partly for non-payment of rent, partly counter-claims by the De Védrines.

He rejects the suggestion that the De Védrines are hapless victims. He believes they are "all in it", especially Guillaume, whom he describes as "Tilly's right-hand man". He adds: "They were almost imprisoned in a house that was boarded and shuttered. No one was allowed in or out. Tilly tried to tell me I was being watched and followed, that he had his own entourage of enforcers. I don't care what happens to any of them, after what they have put me through. They think they are a high-and-mighty, wealthy family but they are just money-grabbing."

Tilly, in prison in south-west France, is refusing to answer questions. But how was he able to commandeer the lives of three generations of a family, described by M. Marchand as "previously joyous, outward-going, successful people"?

The man was born in March 1964 in Bois-Colombes, west of Paris. He has a record of fraud convictions and failed companies in France. In 1999, he began to work for Mr Marchand's former wife, Ghislaine (née De Védrines), who ran a successful secretarial school in Paris. He was rapidly taken into Ghislaine's confidence and, through her, became friendly with her two brothers. M. Marchand said: "I asked her colleagues whether they thought that Tilly and my wife were having an affair. They said, 'No, we think it's far, far worse than that'."

Tilly even tried to recruit M. Marchand. He claimed to be, variously, a "Nato agent", a confidant of George Bush and to have limitless, mental powers. M. Marchand dismissed his claims as fantasy. He believes Tilly "brain-washed" the De Védrines by playing cleverly on their pride as members of a prominent, Protestant aristocratic family. He persuaded them that previous generations of the De Védrines had always been "called" to act for the forces of good against the forces of evil. He even invented a fictitious role as a wartime resistance hero for the elderly matriarch, Guillemette, but told her children never to discuss it with her.

Another technique used by Tilly, M. Marchand says, was to convince his wife and brothers-in-law that he could make them very rich, then persuaded them that they were in imminent, mortal danger from "evil forces" (including M. Marchand). If they pursued their normal lives, they would be killed instantly.

What were the De Védrines doing for all those years when they were locked in the family chateau, now sold? "Nothing. That is the tragedy," said M. Marchand. "My brother-in-law Philippe, told me that they were doing absolutely nothing. Most heartbreakingly of all, he says that my daughter Guillemette used to have moments of lucidity. She would say, 'The best years of my life are being thrown away'. All the same, she remained, somehow, under Tilly's spell."

The Independent tried to contact Charles-Henri de Védrines and one of his sons, who work for The Oxford Garden Company. The company said they declined to speak to the press "for the time being". But Charles-Henri did say: "The truth will come out eventually, then the world will see."