A second tranche of figures has been released from the 2011 census.
The data highlights increased ethnic diversity in England and Wales since the 2001 census, with the proportion of white British people having dropped from 87.5% to 80.5% of the population.
As part of a 3.7 million rise in population over the 10-year period, some 2.1 million new residents were immigrants.
Here are some of the key findings of the Office for National Statistics (ONS) survey in England and Wales, as well as data gathered by the Northern Ireland Statistics and Research Agency (NISRA):
There were four million fewer Christians in England and Wales in 2011 than 10 years earlier, the census found.
Among those who stated a religious affiliation, Christians remained the largest group - 33.2 million, representing 59% of residents. This compares with 37.3 million (72%) in 2001.
The second-most common category was "No religion", comprising more than a quarter of the population (25.1%; 14.1 million), up from 7.7 million (14.8%) in 2001.
The third-most popular category was Muslim, with numbers rising from 1.5 million (3%) to 2.7 million (4.8%) over the 10 years.
All English regions and Wales saw a percentage decline in residents who described themselves as Christians over the period.
The highest percentage of Christians was found in the North East of England, where 1.8 million worshippers represented 68% of residents.
In Northern Ireland, some 48% of people said they were Protestant or had been brought up Protestant - compared with 53% in 2001 - while the number of residents who were Catholic or had been brought up Catholic rose one percentage point to 45%.
More than half of the 7.5 million foreign-born residents living in England and Wales in 2011 had arrived in the last 10 years, the survey found.
Foreign-born residents made up 13% of the population last year - up from 9% in 2001, when there were 4.6 million residents born outside the UK.
The number of UK-born residents rose 1.2 million, from 47.4 to 48.6 million, but this represented a fall from 91% to 87% in percentage of population terms.
For foreign-born residents, there were changes to the most-reported countries of birth over the 10-year period.
In 2001, the Republic of Ireland supplied most foreign-born residents, followed by India, Pakistan, Germany and Bangladesh.
While India topped the table 10 years later, Poland had leaped to second - the number of Polish-born residents having risen ten-fold from 58,000 to 579,000.
Some 86% of residents - 48.2 million people - in England and Wales in 2011 were white, of whom 45.1 million described themselves as white British.
Ten years earlier, 47.5 million white residents comprised 91.3% of the population.
Across the English regions and Wales, the survey found that Wales was the least ethnically diverse area - some 2.9 million whites made up 96% of residents.
The most ethnically diverse area was London, where fewer than half (45%; 3.7 million) of the city's 8.2 million residents were white British.
Since 2001, the number of people of mixed ethnicity had almost doubled to just over 1.2 million in 2011.
There has also been a rise in the percentage of households in England and Wales containing more than one ethnic group.-
Of 16.3 million households comprising at least two people in 2011, two million homes (12%) had members from different ethnic groups in 2011, up from 1.4 million in 2001 (9% of 15.2 million households).
More than 90% of England and Wales residents identified themselves as at least one of: English, Welsh, Scottish, Northern Irish, or British.
In Northern Ireland, some 40% considered themselves British, 25% considered their national identity to be Irish, and 21% thought themselves Northern Irish.
The number of people privately renting homes has almost doubled over 10 years, the census found.
The 3.6 million homes rented from a private landlord or letting agency in 2011, which represented 15% of households, had risen from 1.9 million homes (9%) in 2001.
There was a decline in homes owned with a mortgage or loan, from 8.4 million (39% of households) in 2001, to 7.6 million ( 33%) in 2011.
But there was a rise in homes owned outright, from 6.4 million (29%) to 7.2 million (31%).
Age and sex
The census calculated that the resident population in England and Wales on 27 March 2011 was 56.1 million, with 53 million people in England and 3.1 million in Wales.
This represented a rise - from 52.4 million in 2001 - of 3.7 million.
More than half - 28.5 million - of the 2011 population were women and there were 27.6 million men.
The population aged over 90 rose from 0.7% (336,000) in 2001 to 0.8% (429,000).
There was population growth in all regions of England, and Wales over the period, with the highest growth in London, the East of England and East Midlands.
The population of Northern Ireland rose by 125,600 to 1.8 million from 2001 to 2011.
Asked to assess their general health on a five-point scale - very good, good, fair, bad or very bad - more than 80% of people (45.5 million) declared themselves in good or very good health.
Just 6% of people (3.1 million) described their health as bad or very bad.
Residents in the North East of England reported both the lowest level of very good health (44%), and the second-highest percentage - 7% - for bad or very bad health, behind Wales's figure of 8%.
The census also found that 10% of people (5.8 million) provided unpaid care for someone with an illness or disability - the same percentage as in 2001 (5.2 million).
But 37% of those carers in 2011 (2.1 million) were giving 20 hours or more of their time a week, up from 32% (1.7 million) in 2001.