It started, as a number of the world's great religions have done, with a small group of friends and a persuasive idea: why should atheists miss out on all the good things churches have to offer? What would happen if they set up a "godless congregation" that met to celebrate life, with no hope of the hereafter?

Eight months after their first meeting in a deconsecrated church in north London, the founders of the Sunday Assembly have their answer: on Sunday they will announce the formation of satellite congregations in more than 20 cities across Britain and the world, the first wave of an expansion that they believe could see 40 atheist churches springing up by the year and as many as 1,000 worldwide within a decade.

From Glasgow, Leeds, Bristol and Dublin, to New York, San Diego and Vancouver, to Perth, Melbourne and Sydney, groups of non-believers will be getting together to form their own monthly Sunday Assemblies, with the movement's founders – the standup comedians Sanderson Jones and Pippa Evans – visiting the fledgling congregations in what they are calling, only partly in jest, a "global missionary tour".

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Nick Spencer, research director of Theos, a thinktank looking at religion's role in society, says the growth of the movement may appear striking but it is not necessarily new. "This contemporary idea of people who are not religious but wanting to maintain some kind of church-like existence has got form. We've been here before."

Spencer, who will publish a book next year on the history of atheism, sees echoes of the late 19th century, when hundreds of "ethical unions" were founded in response to the growing atheism of the times. The movement, he says, similarly concentrated on good works and community around a recognisably church-like liturgy, but petered out within a generation or two.

"The reason for that was because you need more than an absence to keep you together. You need a firm common purpose. What you can see in these modern-day atheist churches is people united by a felt absence of community. I suspect what brings them together is a real desire for community when in a modern, urbanised individualised city like London you can often feel very alone. That creates a lot of camaraderie, but the challenge then becomes, what actually unites us?"

Esther Addley | Read the article in full on theguardian.com