Thousands of former Muslims in Britain fear violent revenge for leaving the Islamic faith and others are afraid to admit they no longer believe amid a "tsunami of atheism", according to the head of a support group for ex-Muslims.

Maryam Namazie, founder of the Council of Ex-Muslims of Britain, has said that more needs to be done to help those who have renounced their Islamic faith.

Namazie was speaking ahead of an ITV documentary scheduled for 13 October, Exposure, which explores the lives of ex-Muslims faced with abuse and discrimination.

She told The Independent: "There is a large group of people who are not seen and heard. Many young people living in Britain have left Islam and are facing huge ostracisation and isolation from their communities as a result.

"They're very often silenced or they're living closeted lives. They're still acting as Muslims, still wearing the veil and still going to the mosque, but they're really atheist."

Namazie, an Iranian-born activist and ex-Muslim herself, described the "hidden challenge" of being in a minority within a minority.

"It's a hidden challenge for people here in Britain," she said. "It's framed in this context of identity politics, racism and any criticism means you're racist. But we are minorities within minorities and we have a right to speak and live our lives the way we want the same as anybody else.

"There's a tsunami of atheism in Muslim communities across the globe and in Britain. It's a time bomb that can't be seen but is exploding. There needs to be more recognition so people get the support they need."

Exposure reveals that many ex-Muslims are at risk of suicide or self-harm as well as physical and psychological abuse from family members.

One ex-Muslim, Sadia, whose brother killed himself, tells the documentary that his death was partly due to his atheism and the fact that he felt sidelined and misunderstood by his community all his life.

She says: "I feel like when you leave Islam, your intelligence gets attacked. They make you feel like you're stupid for making such a decision, which he felt like his entire life. Leaving Islam, becoming an ex-Muslim, all of a sudden you feel like you're dirty, and you become unimportant within the community."

Namazie told The Independent that the problem is exacerbated by the international situation, and Muslim extremists.

She said: "There are international links with what's happening here. Ex-Muslims are being killed in Bangladesh, then you've got Islamists here threatening Bangladeshi bloggers who have fled to Britain.

"We also need to recognise that many religious leaders in this country are not representative of the Muslim community but really representative of the Islamist movement that is encouraging this discrimination against ex-Muslims."