Fewer than half the people of London are white British, the 2011 census shows.
Latest figures show 45% of Londoners describe themselves as "white British" - a drop from the 58% in 2001.
The capital also had both the largest proportion of residents born outside the UK (37%) and non-UK nationals (24%.)
A spokesman from the Migrants' Rights Network said there had been an influx of migrants in the past 10 years.
The 2011 census shows 86% (48.2 million) of residents of England and Wales are white, and 80% of them white British (45.1 million).
In London 3.7 million out of 8.2 million usual residents are white British, the figures show.
The census shows London is the most ethnically diverse area in England and Wales.
There are 175,974 white Irish; 8,196 white Gypsies or Irish travellers, and one million "white other", according to the figures.
The London statistics include 102,000 mixed white and Asian people; 119,000 mixed white and black Caribbean; 119,000 other mixed, 542,000 British Indian; 224,000 British Pakistani and 222,000 British Bangladeshi.
There are 399,000 other Asians, 574,000 British Africans and 345,000 British Caribbeans in the capital, along with 170,000 other black people; 106,000 Arabs and 175,000 from other ethnic groups.
The Migrants' Rights Network spokesman said there would be a "a lot of different explanations" about who the migrants were and their reasons for being in London.
"A lot will have arisen from new European Union (EU) members in part after 2004 when countries from Eastern and Central Europe joined," he said.
In 2004, the EU took in new members the Czech Republic, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.
"But it will also reflect the fact that London is an international, cosmopolitan city," the Migrants' Rights Network spokesman said.
"Many industries such as banking will be attracting global talent and that will be reflected in the numbers we are seeing," he added.
Agnieszka Ciepłucha, 29, moved to London from Poznań, Poland in 2008, with her Brazilian husband.
"It was the only option for us between Brazil and Poland and we both spoke English," she said.
She works at the Polish Cultural Institute in central London.
She said that after 2004 it was easier for Poles to find hospitality work in the "enormous" sector in London than it was at home.
'Less pay in Poland'
She said: "There was less pay in Poland and fewer jobs."
She plans to stay about another five years, she said.
The census also showed London was the only region where the number of vehicles was lower than the number of households in 2011.
London was the only region where the number of vehicles was lower than the number of households in 2011.
It also had the highest percentage of residents who did not state a religion - 8% (693,000) did not answer.