Purnima Rani, a 12-year-old Hindu girl, is terrified and breaks down frequently as she describes what happened 18 months ago in the village of Perba Delua in Bangladesh.
"Nearly 30 people came to our house. I recognised many of them as my neighbours. They beat my mother almost senseless. I begged them to stop. They dragged me outside. I resisted but they hit me with sticks. I shouted to my sister to save me but they beat her too. I cannot tell you what happened next."

Purnima was gang-raped and her family found her unconscious three hours later in a field a mile from the village. Four young men, all supporters of the government and its coalition partner, the fundamentalist Jamaati-e-Islami party, were arrested but have not been charged.

But the ordeal did not stop there. The family's hairdressing business was twice looted, her elder brother was beaten and is expected to lose his sight, and they have now all fled the village after threats that they would be killed.

Her father has been offered bribes to drop the case and Purnima, one of the few victims of Bangladeshi sectarian violence who is prepared to talk openly, is now in hiding. "I want justice, not money," she says.

Serious attacks on and persecution of religious minorities by Islamic fundamentalists are increasing, and despite a detailed dossier on 18 months of persecution of religious minorities, and women in particular, the British government calls Bangladesh a "generally safe" country. Amnesty International says this makes "no sense".

Thousands of Bangladeshis are fleeing, a few wealthy ones applying to go to Britain and continental Europe. Those who arrive in Britain will almost certainly be sent back. But the Guardian has uncovered compelling evidence that in declaring Bangladesh in effect free of internal problems Britain is turning a blind eye to atrocities committed by fundamentalists.

Evidence is emerging that the oppression of minorities is becoming systematic. Bangladesh, which is 85% Muslim but has a long tradition of tolerance to religious minorities, is, say local organisations, being pushed towards fundamentalism by the Jamaat-e-Islami, which is growing rapidly in rural areas with the deepest poverty and runs two key ministries.

"This is like a silent revolution. We are returning to the dark ages," a leading lawyer said, asking not to be named.

"I think the backdrop is being created for the introduction of strict sharia laws. You see extremist rightwing fundamentalists infiltrating every professional area, in the appointment of the judiciary, the law, medicine and in education. They are capturing key positions in government, the universities and institutions."

Britain has seen the dossier of human rights abuses, which is backed by evidence from local and international development groups.

In the village of Fhainjana, a mob of 200 fundamentalists recently looted 10 Christian houses, allegedly assaulting many women and children. Christians were seriously beaten and others molested after refusing to give money to thugs in the village of Kamalapur, near Dhaka. In Deuatala Bazaar, gangs of young men with knives told Hindus to leave. Hundreds fled.

Many villages are said to be now empty of minorities. Elsewhere, Hindus have been burned alive and gangs have desecrated temples.

Rosaline Costa, director of the human rights group Hotline Bangladesh, says that the British government is well aware of the situation. "They must think we are stupid. It says there is communal harmony, but this is a lie. Documents showing the scale of the atrocities on minorities have been sent to all governments. There are many genuine asylum seekers."

Thousands of Bangladeshis are thought to have crossed the border to India in the past two years. It is impossible to verify numbers because New Delhi will not release records, but Dhaka's statistics show the Muslim majority increasing dramatically and the Hindu, Buddhist, Christian and other minorities declining.

In western Bangladesh, where the Jamaat-e-Islami is particularly strong, many villages have been deserted by minorities. "In my village of Sri Rumpur, near Khulna, there are no Hindus left," said a man who asked not to be named. "They have all been driven out by people threatening to torture them or demanding money. People who raise their voices are threatened. It's a kind of systematic ethnic cleansing."

Toab Khan, editor of the independent newspaper the Daily Janakantha, said: "Repression of people who publicise human rights violations is growing. We have reported communal violence from the beginning. Our head office has been bombed, our agents have been threatened and beaten up. The government has withdrawn all its advertising and is pressurising and harassing reporters and the owner."

Attacks on press

Last month three newspaper editors were arrested after publishing a letter critical of the government's human rights record. BBC and Channel 4 film-makers have been detained. Shariar Kabir, a film-maker and human rights activist, was charged with treason and jailed for 59 days for writing about torture and interviewing Hindu families who told him they were fleeing the country.

The Bangladeshi government, which has admitted that some atrocities have taken place, argues that the violence is not religiously motivated. But it has directly attacked western-funded NGOs working to increase women's rights and strengthen the voice of the poor in minority communities.

In the past 18 months British and European aid to five main NGOs has been frozen, ostensibly pending an investigation but almost certainly because they have worked with the poor to strengthen women's rights. The UK Department for International Development's office in Bangladesh has protested.

"Up to £40m in grants directed at relieving poverty for 2.8m families is affected. Millions of the poor are being denied help for ulterior motives," Kabir Choudhury, president of the South-East Asia Union against Fundamentalism, said.

Leading Islamic scholars are appalled by the repression and the rise of fundamentalism. "What we are seeing is the Talibanisation of Bangladesh," Maolama Abdul Awal, former director of the Bangladesh Islamic Foundation, said. "If we allow them to continue ... [minorities] will be eliminated. Bangladesh will become a fascist country."

An NGO director said: "I am being called a terrorist. They telephone me personally demanding money, saying they will push me out of the country and that my children will be killed ... They intend to wipe us out. I do not understand why the British government is turning a blind eye to what is happening."