The proportion of people in England and Wales calling themselves Christian has dropped below half for the first time.
The 2021 census data, released on Tuesday, suggests a huge increase in the number of people that do not identify as religious, compared to a decade ago.
Just 46.2 per cent of people consider themselves to be part of the Christian faith - in 2011, the figure was 59.3 per cent.
Around 37.2 per cent said they had no religion at all, up by a quarter from the last results.
Despite Christianity still being the largest grouping, the Guardian newspaper has now labelled England and Wales "minority Christian countries".
Peter Brierley, a church consultant, told Premier Christian News: "It's a fall that is greater than many people were expecting a couple of years ago. In a meeting I participated in with some of the academics, they thought it would not even go below 50 per cent.
"Linda Woodhead, a professor of sociology, recently expected the number to go down below the 50 per cent mark, but I think even she would have found that the 46 per cent was still lower than anticipated."
The Census question was voluntary, with participants asked what their religion is as opposed to specific practices.
"Does it imply that Christianity is declining?" Mr Brierley continued. "The answer is, unquestionably, yes. There's no doubt about that; but we have to look at which bits are declining.
"Christianity is not universally declining. There are many growing churches, and many new churches; not sufficient to offset the decline but simply to say not everything is going in the same direction."
Mr Brierley says it is institutional churches that are the worst hit by falling congregation numbers.
He described a "major decline" in members of the Church of England, the Catholic Church, the Methodist Church and United Reformed Church.
However, independent churches - particularly those with a large number of ethnic minority attendees - are seeing growth.
Despite Mr Brierley's reassurances that the Church is still holding its own, non-religious groups are taking the census results as a win.
Steven Evans, CEO of the National Secular Society, said: "I think that it's really a watershed moment for the UK not being a majority Christian country.
"I think that's particularly important because for in a country with an established state church - I think that poses some pretty fundamental questions.
"The overall picture is one of increasing irreligiosity, but it's also one of growing diversity as well. So I think the privileged and the prominent role that we see for Christianity in public life really needs to be questioned now."
The figures came as a shock to some sociologists, but the Archbishop of York was unsurprised by the news.
Most Rev Stephen Cottrell said: "We have left behind the era when many people almost automatically identified as Christian but other surveys consistently show how the same people still seek spiritual truth and wisdom and a set of values to live by."
He maintains that the Church is a force for good during an increasingly difficult time, and that many will still experience an outpouring of love from the Christian community.
"This winter - perhaps more so than for a long time - people right across the country, some in desperate need, will be turning to their local church, not only for spiritual hope but practical help," he continued.
"We will be there for them, in many cases, providing food and warmth. And at Christmas millions of people will still come to our services."