The steady decline of religion in the Western world is being mirrored by the growth of so-called atheist churches, statistics show.

According to the Washington DC-based Pew Research Center, the religiously unaffiliated are now the second-largest religious group in North America and most of Europe.

A study by theology professor Stephen Bullivant, from St Mary’s University in London, found that more than half of the UK’s population does not identify as religious. “The rise of the non-religious is arguably the story of British religious history over the past half-century or so,” Bullivant says in the introduction to his report, titled The ‘No Religion’ Population of Britain.

At the same time, there has been a growth in the number of atheist churches, which aim to replicate much of the church service atmosphere but without the religion.

A “small subset of those people who have lost their faith in a supernatural being still want the community spirit and behavioural norms that go with religious experience”, Phil Zuckerman, professor of sociology and secular studies at Pitzer College in California, told The Economist.

But what are atheist churches and what do they offer the people who attend them?

What are they?

Atheist churches aim to provide some features of a religious congregation - fellowship and collective enjoyment - while forgoing any belief in a deity or the supernatural.

In recent years, the most widely publicised and globally spread atheist church has been the Sunday Assembly, launched in London in 2013 by comedians Sanderson Jones and Pippa Evans. “It now exists in 55 outposts, across Britain, continental Europe, North America and Australia, with a total of about 3,500 regular attendees,” reports The Economist.

Under the motto “live better, help often, wonder more”, a typical Sunday Assembly “consists of a singalong (pop songs rather than hymns), a secular reading, a talk that helps the congregation followed by a moment of reflection, then tea and cake”, says The Daily Telegraph.

The London congregation has attracted a wide range of speakers, from TV presenters such as Loyd Grossman, Sandi Toksvig and Dan Snow to comedians Arthur Smith and Marcus Brigstocke.

What are they for?

“Obviously, they appeal to people whose world views reject the supernatural,” says The Economist. “But in their own way they are (as they themselves say) doing what all religious communities do, but simply without gods and the supernatural.”

Surveys of assembly-goers suggest that the great majority feel greater “life satisfaction” through participation.

One of the proponents of the Sunday Assembly, philosopher and writer Alain De Botton, argues for a new breed of secular therapists to take the place of the priesthood. However, although he supports the concept of atheist churches, De Botton told the BBC: “It should never be called that, because ‘atheism’ isn’t an ideology around which anyone could gather. Far better to call it something like cultural humanism.”

Can they really be called churches?

“I don’t expect much objection from religious communities. They are happy for us to use their church model,” Sunday Assembly founder Sanderson Jones has previously told Salon magazine.

But “only someone who already feels entitled to the Christian ‘model’, and who doesn’t understand why it might be a sacrilege to appropriate those forms and gestures, would assume as much”, says The Guardian’s Adam Brereton.

Describing the Sunday Assembly’s growth as “part of the long, inglorious march of gentrification”, Brereton argues that atheist churches aren’t “much deeper than consumption, dressed up as community, for yuppies who want to feel good”.

Professor Zuckerman is more equivocal about whether the events constitute a religion. “If you define religion as just belief in god(s) or supernatural beings, then it’s not religious,” he says. “But if you define religion more broadly as having a belonging component, and a behaviour component, then it does...fall under that umbrella.”