The number of Christians in England and Wales has fallen by more than four million in a decade, while the foreign-born population has jumped, according to the 2011 Census.
Christianity was the only religion to see a decline in believers since 2001, while the fastest-rising faith group, Islam, has seen its numbers rise by 1.2 million, the findings of the latest instalment of the national survey show.
The Census, which gave the total population of England and Wales as 56.1 million, also found that the number of people with no religion had doubled in a decade.
Christianity remains the largest religious group at 33.2 million, or around six in 10 of the population, but around one in four people in England and Wales now classify themselves as having no faith.
The British Humanist Association said the results showed there had been a "significant cultural shift" in a society where "religious practice, identity, belonging and belief are all in decline… and non-religious identities are on the rise".
The Reverend Arun Arora, the Church of England director of communications, said: "Obviously the fall in those choosing to identify themselves as Christians is a challenge. We need to look closely at the fuller figures published next year and to reflect on what these tell us."
Foreign-born people now make up 13 per cent of the population in England and Wales, rising from 4.6 million in 2001, or 9 per cent of the population, to 7.5 million last year. Just over half of the foreign-born population, or 3.8 million, arrived in the past 10 years.
During the same period, there was a fall of nearly 7 per cent in the number of people classifying their ethnic group as white British.
The largest rise in an ethnic group in the past decade was in the white other category, up 1.1 million, to 2.5 million, reflecting more than half a million Poles who migrated into England and Wales, the Office for National Statistics said.
In London, the most ethnically-mixed area of the country, more than one in three of the population, or 37 per cent, is now foreign-born, and the proportion of the population which classifies itself as white British has fallen below half, to 45 per cent, for the first time. The statistics show an increase of nearly 600,000 in the number of people classifying themselves as of mixed ethnicity to more than 1.2 million.
India had replaced the Republic of Ireland as the biggest migrant community, with Pakistan retaining third position. Census director Guy Goodwin said: "It is a picture of big change since 2001 – and of a population that is increasingly diverse."