For the first time fewer than half of people in England and Wales describe themselves as Christian, the Census 2021 has revealed.
The proportion of people who said they were Christian was 46.2%, down from 59.3% in the last census in 2011.
In contrast the number who said they had no religion increased to 37.2% of the population, up from a quarter.
Those identifying as Muslim rose from 4.9% in 2011 to 6.5% last year.
People were also asked about their ethnic group and national identity - the responses of which were released in the results just published.
The census is carried out every 10 years by the Office for National Statistics (ONS).
People were asked the broad question what their religion was rather than being asked more specifically about their beliefs or religious practices, in the voluntary question included in the census since 2001.
Ticking "no religion" does not mean having no beliefs, says Prof Linda Woodhead, from King's College London.
"Some will be atheist, a lot will be agnostic - they just say, 'I don't really know' - and some will be spiritual and be doing spiritual things." she said.
Separately when people were asked about their ethnic group, 81.7% of residents in England and Wales identified as White, down from 86.0% a decade earlier, according to the census.
And 74.4% of the total population identified as White as well as English, Welsh, Scottish, Northern Irish or British.
The next most common ethnic group was Asian, Asian British or Asian Welsh accounting for 9.3% of the overall population - 5.5 million people, up from 4.2 million.
The number of people identifying as Black, Black British, Black Welsh, Caribbean or African was 2.5% of the population, up from 1.8%, taking the figure from 990,000 to 1.5 million.
One in 10 of households across England and Wales are now made up of people from two or more different ethnic groups - an increase from 8.7%.
Leicester has become one of the first cities in the UK where people identifying as white are no longer the majority - with 41% compared to 51% in 2011.
In terms of national identity, among those who described it as not being the UK, the most common response was Polish, followed by Romanian.
In terms of religion, London is the most religiously diverse region of England, with just over 25.3% of people reporting a religion other than Christianity.
And south-west England is shown to be the least religiously diverse region, with 3.2% selecting a religion other than Christian.
The figures also showed differences in nations - in England alone, 37.2% of people said they had no religion, while in Wales this rose to 46.5% from 32.1% in 2011.
Following the announcement, the Archbishop of York said the country had "left behind the era when many people almost automatically identified as Christian".
The Most Rev Stephen Cottrell said: "It's not a great surprise that the census shows fewer people in this country identifying as Christian than in the past, but it still throws down a challenge to us not only to trust that God will build his kingdom on Earth but also to play our part in making Christ known."
He said that, facing a cost-of-living crisis and war in Europe, people still needed spiritual guidance, adding: "We will be there for them, in many cases, providing food and warmth."
Chief executive of Humanists UK Andrew Copson added the figures should be a "wake-up call which prompts fresh reconsiderations of the role of religion in society".
The census explores how British society is being shaped from people's answers to questions about themselves, their household and their home.
The results help organisations make decisions on planning and funding public services including transport, education and healthcare.
The 2021 survey, carried out on March 21 last year, was filled out by more than 24 million households across England and Wales. More data from the census is set to be published in stages over the next two years.
Scotland's census was due to take place in 2021 but was delayed by a year due to the Covid pandemic.
Source: BBC
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