In November 1994 an American woman known as Janice Doe filed a $10m lawsuit against the Tibetan lama Sogyal Rinpoche, charging him with sexual, mental and physical abuse. The case was dealt with out of court and Janice Doe signed a non-disclosure agreement in return for a cash settlement.

Sogyal denies allegations of abuse, but fresh evidence against him was recently aired in an investigative documentary called In the Name of Enlightenment, broadcast on Vision TV in Canada. A beautiful young woman identified as Mimi described an abusive sexual relationship. She was the first person claiming direct experience of Sogyal's exploitative attentions to go public since the 1994 lawsuit.

Sogyal (surname Lakar – Rinpoche is a title that means "precious one") is the frontman for a Tibetan Buddhist organisation called Rigpa, which has a worldwide reach with 130 centres in 41 countries. He has a bestselling book, The Tibetan Book of Living and Dying, to his name and he starred alongside Keanu Reeves in the movie Little Buddha. Sogyal is a formidably successful guru – probably the best known Tibetan after the Dalai Lama. His trajectory into Buddhist superstardom suffered only a temporary setback following the Janice Doe lawsuit – despite the fact that lurid rumours about his sex life circulate on the internet with increasing volume and persistence.

The allegations raise a wider question: why are victims of sexual exploitation by charismatic religious leaders reluctant to denounce their abusers? In the Canadian documentary, Mimi highlights the Stockholm syndrome – a term used to describe the paradoxical reactions of individuals who bond with their abusers. "The person beating us, she says, "is also the only one giving us affection – and food and a roof over our heads."

Sociologist Amanda van Eck is deputy director of Inform, the cult information resource at the London School of Economics. She says fear is probably the main reason why women stay silent: "In some groups there has been fear of retribution," she says, "which means they don't want to speak publicly. In other cases, which may overlap with fear of retribution, they are fearful of negative consequences – damnation, of not being saved, of possession by evil spirits, of being attacked by negative forces and so on."

If the outside world has been demonised by cult leaders, Van Eck says, women may also be fearful that no one can be trusted.

Many women who have described abusive sexual relationships anonymously on internet forums refuse to come out of hiding because they want to move on, rather than relive traumatic periods in their lives. Some also feel a need to protect their families.

In my personal experience, there are two taboos in Buddhist organisations, both of which have merit and both of which can be used as manipulative tools. One of them is an injunction against gossip – useful when trying to establish a calm mental state, but also useful to prevent the circulation of critical comment.

The second is samaya – the bond of loyalty that is one of the key tenets of Tibetan Buddhism. It supports the relationship between teacher and neophyte, but it can be deployed unscrupulously as a threat – break your samaya and attract dire consequences to yourself and your loved ones.

Another factor is that acceptance into the inner circle around an important guru delivers high status within the organisation. Women are persuaded to view the master as a deity and to be compliant with his wishes and whims, to undertake a punishing workload and be available for sex on demand. They are separated from family and friends, discouraged from contact with the outside world and persuaded to see the organisation as family with the guru (confusingly as father-lover) in absolute power and control. By the time women realise they are being abused, exploited and embedded in a coercive cult, it is often too late for them to extricate themselves. Their investment is total and their chances of making lives for themselves beyond the organisation have dwindled into non-existence.

Whether or not Sogyal's relationships were abusive, as claimed, they raise another question: how does a short, overweight, Tibetan lama manage to attract beautiful young western women? The answer is rooted in the mystique of tantra – the only Buddhist tradition that includes sexual union in the path that leads to enlightenment. Professor Geoffrey Samuel from Cardiff University explains: "In the third initiation of the highest yoga tantra, sexual union is introduced as a parallel to the experience of enlightenment. It creates certain sensations that help towards experiencing the state of ultimate realisation – in other words Buddhahood."

But Samuel says that although this arcane version of sacred sex is present in Tibetan Buddhist scriptures, it should not be confused with the modern neo-tantra movement and nor is it appropriate for recent converts to Buddhism."People should have a health warning" he says. "An elderly guru seducing a young woman probably isn't doing it to assist her towards enlightenment."

Tibetans outside Tibet are refugees who feel constantly under threat from forces beyond their control. Their social conventions include a taboo against criticising lamas. The Dalai Lama is constrained by this and so too are the majority of other lamas teaching in the west. They have closed ranks around Sogyal, regardless of their misgivings about the allegations against him. A more cynical view of this apparent conspiracy of silence hinges on the fact that Sogyal pulls in a lot of money – some of which is channelled into Tibetan worthy causes.