Atheism are growing in the US while Christians becoming warm.

At first glance, the group of scruffy-looking students could be attending a meeting of any old debating club, but as they begin to speak it soon becomes clear that they all share the same secret.

A shy young woman is among the first. She admits she is still a long way from telling her parents the truth about herself. “My closest friends know,” she says, “but where I come from, I only know one other person like me, who was a teacher. I will tell my parents in the end, I can’t now; at least, not until I am financially independent.”

Going around the circle, each member shares their story and says whether or not they are “out” of the closet.

But while they use the lexicon of the gay and lesbian movement they are not speaking of their sexuality: they are not gay or lesbian, but atheist and agnostic.

A decade ago, a group non-believers meeting publicly on a university campus like this one at Virgina Tech would have been rare, but over the last five years the number of student “freethinker” groups in the US, has begun to snowball: from 100 in 2007 their number has leapt to more than 350 today, according to the nationwide Secular Student Alliance.

Their growth reflects a rapid shift in attitudes towards religion in America among young people, with one recent Pew poll finding that more than one third of Americans aged 18 to 29 now say they have “no religious affiliation”, compared with less than 10 per cent of their grandparents’ generation.

While America still remains outwardly far more religious than Europe, the sudden rise of the “nones”, as they were dubbed by the Pew Forum on Religion and Public Life, has raised the question of whether the US is on the cusp of a dramatic sea-change in attitude towards religion in public life.

The recent shift in the gay marriage debate is evidence, say secularists, of how fast entrenched public attitudes can change: a decade ago just 30 per cent of Americans supported gay marriage, today the figure is consistently over 55 per cent. A decade from now, will attitudes to religion have followed suit?

And yet despite the softening approach of the younger generation towards religion, in this fiercely Bible-minded corner of Virginia, many atheists and agnostics still feel they must live in the shadows.

In two days of interviews at least half of the avowed non-believers declined to be named in the Telegraph, citing fears they would be ostracised by friends, family, churches and even their employers.

The Virginia Tech group contains a broad spectrum, from life-long atheists who grew up in sceptical families to home-schooled Baptists, evangelical Catholics and even a young man who was brought up in a Dominionist cult dedicated to establishing a Theocracy in America.

Caroline – not her real name – is a graduate research chemist who is about to hit the job market and is afraid that her atheism will be held against her.

“I’m more concerned about getting a job than losing one,” she said. “I know they Google you and while I can’t hide my atheism, I don’t really want to advertise it.

“If the person hiring is a person of faith – which is more likely than not around here – that could easily be the difference between a job and no job. And I have student loans. I need a job.”

She is not alone in her fears. Another student who is applying for graduate school told how his father recommended he delete any references to atheism from his Facebook page in case it spoiled his chances. He rejected the advice on principle, but remains unsure what the consequences will be.

For others members, the biggest fear is being shunned at home. “I’ve lost a lot friends,” said John, a graduate student in his thirties who grew up being home-schooled by his Southern Baptist parents but gave up his faith after an intellectual rebellion against the church’s Creationist teaching.

As a sign of how strong religion remains, polls show that a third of Americans still believe in the most literal form of “young earth” Creationism – that the world was created in seven days 6,000 years ago, and that all living animals were saved by Noah in his ark.

“I wish there had been groups like this when I was an undergraduate,” John added. “It has taken me a long time to rebuild my life after ’coming out’. My parents know I don’t believe, but most of their friends do not.”

The difficulty of speaking openly about non-belief is reflected in wider American society. While atheism is more often expressed than it used to be – thanks partly to prominent atheists like Brad Pitt, the actor, and Mark Zuckerberg, the founder of Facebook – there is still only one declared non-believer among 535 members of the US Congress.

And despite changing attitudes among the Millennial generation, Christian groups caution against reading too much into the rise of the “nones”, seizing on the fact that surveys show a majority of that group still believe in God, or some kind of higher power – even if they don’t go to a formal church.

The continued power of that church is visible at Lynchburg, some 90 minutes’ drive north of Virginia Tech. The town is home to Liberty University, a college for Evangelical Christians opened by Jerry Falwell, the 1970s televangelist whose Moral Majority helped drive the Reagan Revolution and the resurgence of the Religious Right.

Religiosity might be declining among the young, but the university, now run by his son, is booming like never before with some 13,000 students on campus, nearly 100,000 more online and a $1.2 billion endowment in the bank.

“From our perspective, we don’t feel like we’re a dying breed, we feel like we’re on a crest of a wave,” said Johnnie Moore, a senior vice president and well-known preacher at Liberty who maintains that atheists are not becoming more numerous, just more vocal.

“We’re not seeing a vast de-conversion of people to a more Godless view of life,” he said, pointing to the rise of urban mega-churches with 40,000 member congregations.

“What we are seeing is a small group of loud atheists with a platform, empowering people who were perhaps already atheists to speak up more.”

Others are not so sure. While two-thirds of the religiously unaffiliated say they are “religious or spiritual in some way”, some 88 per cent of that group say they are not looking for an organised religion.

The lack of clarity about what the “nones” really believe allows both groups – religious and the secularists – to claim them for their own, when in reality many simply sit in between. Undefined, and happily so.

What this means for American 30 years from now is unclear, admitted Dan Linford, the president of the Virginia Tech freethinkers and a graduate student in the philosophy of religion, but he believes that gradual trend towards more openness about religious non-belief will bring social change, just as it has for gays and lesbians.

“At present the Religious Right has a tremendous amount of power, but they are getting older,” he said. “Surveys show young Americans are rejecting institutional religion because they identify it with the Religious Right and values that they find off-putting, and frankly, immoral.”

Other studies have argued that the polarisation of American politics has turned off many young people from institutional religion since Republicans, who fare poorly among young voters, have been conflated with religious groups considered “judgmental, homophobic, hypocritical, and too political”.

Atheists at Virginia Tech – and two young, closet atheists at Liberty interviewed by the Telegraph – also argued that the social shackles that prevent them going public with their atheism could mean that atheism and agnosticism is actually far more prevalent than the polls suggest.

Brian Farrell, a 22-year-old computer science graduate who grew up a Christian but is now an “out” atheist, said that for many of his age group it was easier simply to “go along with religion” than to risk being left out in the cold.

“The stakes are high,” he said. “Do I want to be supported by my friends and family, or am I going to risk being kicked out of clubs and organisations? It’s tempting just to avoid the whole issue. I would put 20 or 30 per cent of my friends growing up in that category.”

A former Liberty student turned atheist, who works at the university but asked not to be named since staff are required to be believers, volunteered a similar estimate.

Asked how many of his friends growing up in an Evangelical Christian community had moved away from their literalist faith, he replied “between a third and a half”, although few had openly declared it.

Mr Linford is wary of making sweeping predictions about whether attitudes to secularism will follow the same trajectory as those towards gay marriage, but believes that significant changes lie ahead.

“Young people are becoming increasingly non-religious, which doesn’t mean their giving up on supernatural beliefs altogether, but it does mean they check the ’none’ box when asked about religion,” he said.

“In 20 or 30 years’ time it is possible we will look back on today and say these were the death throes of the American religious Right.

“But even if that is not the case, atheists and agnostics will increasingly enter politics and have a larger voice in this country. An atheist president is then not an impossibility.”