The share of the English and Welsh population who said they were white in the 2021 census dropped to 81.7% from 86% in 2011, while the proportion who described their ethnicity as “Asian, Asian British or Asian Welsh” rose to 9.3% from 7.5%.

England and Wales’s population of people who described themselves as “Black, Black British, Black Welsh, Caribbean or African” rose to 4% from 3.3%.

Britain’s Office for National Statistics said the shifts in ethnic composition reflected “differing patterns of ageing, fertility, mortality, and migration”, and possibly changes in how people classed themselves.

Census data released earlier this month showed the foreign-born population in England and Wales had risen by 2.5 million over the past 10 years, reflecting significant immigration from eastern Europe, south Asia and Africa.

Data for Britain as a whole are unavailable, as Scotland’s government delayed the census there by a year because of the Covid-19 pandemic.

Tuesday’s census data showed an especially sharp drop in the share of people in England and Wales who described themselves as Christian, which fell to 46.2% in 2021 from 59.3% in 2011.

This drop was mirrored by a big increase in people saying they had no religion, which rose to 37.2% from 25.2%.

Islam was the second most common religion – followed by 6.5% of the population and up from 4.9% in 2011 – while Hinduism was the third most common at 1.7%. Sikhs made up 0.9% and Jews 0.5% of the population.

The census also allowed people to give more detail on their ethnicity.

Among people who said they were white, the proportion who also said they were “English, Welsh, Scottish, Northern Irish or British” dropped to 74.4% from 80.5% in 2011, while “White: Other White” rose to 6.2% from 4.4%.

For people of Asian ethnicity, the numbers who stated an Indian, Pakistani or Bangladeshi heritage all rose, while the proportion with a Chinese background was stable.

Fewer Black people described themselves as being of Caribbean heritage, while the main African backgrounds given were Nigerian, Somali and Ghanaian.

London remained the most ethnically mixed part of England and Wales. Only 36.8% of Londoners described themselves as “White: English, Welsh, Scottish, Northern Irish or British”, down from 44.9% in 2011.