Britain will be the Western world's most ethnically diverse nation after 2050, according to an explosive academic study.
It lays bare the effect of decades of immigration and claims that white Britons will be in a minority by 2066.
A mass influx of migrants has given the UK the fastest-rising percentage of ethnic minority and foreign-born populations.
The report - which also reveals the huge impact of Labour's open-door policy to immigration between 1997 and 2010 - says foreigners and non-white Britons living here will double by 2040 and make up one third of the UK population.
Report author Professor David Coleman said: "On current trends European populations will become more ethnically diverse, with the possibility that today's majority ethnic groups will no longer comprise a numerical majority."
The findings mean that the UK could overtake the United States as the world's melting pot, with fewer people describing themselves as British or white.
The projection comes after David Cameron sought to reassure voters that the influx of migrants from Bulgaria and Romania will be "nothing like" the levels seen when Poland joined the European Union.
The professor of demography at Oxford made his findings from a study of international population projections, carried out for the academic organisation Migration Observatory.
In the study, minorities are classed as people who also describe themselves in censuses as Irish or another nationality, as well as by their skin colour.
Prof Coleman said migration has become the "primary driver of demographic change".
According to the data, around a fifth of people in the UK are non-white or non-British. But this is expected to rise to a quarter by 2025, a third by 2040 and reach up to 38 per cent by 2050.
The increase from 2010 to 2050 in the UK - by 22 percentage points - is the highest of the main western countries analysed.
Over the same period, the proportion of non-whites and migrants in Denmark will rise from 10 per cent to 14 per cent.
Declining birth rates among white Britons is another factor.
In England and Wales, 25 per cent of births are to foreign-born mothers, the report said. A similar trend is seen in France and Germany.
We now need concrete
proposals to reduce
immigration. No less
important is the task of
integrating such huge
numbers into society"
Andrew Green, from
The calculations are based on the current net rates of immigration, which have been running at more than 200,000 a year.
Prof Coleman pointed to a study which suggests "the crossover for the whole country when the combined population of all ethnic minority groups together would exceed the population of white British will occur at around 2066.
However, he says the Coalition's plans to limit net migration could have an enduring effect on the impact on the make-up of the British population. Immigration campaigners yesterday raised concerns about newcomers' ability to integrate into society, and their impact on the health and education systems.
The UK's population is estimated to hit 77 million by 2051.
Andrew Green, from campaign group MigrationWatch, praised the importance of the study.
He said: "It brings out the consequences if the mass immigration triggered by Labour is not rapidly brought under control.
"Nearly four million immigrants have arrived since 1997 and the impact is felt in maternity units, housing and primary schools.
"We now need concrete proposals to reduce immigration. No less important is the task of integrating such huge numbers into society."
The Government has promised to control the impact of new arrivals from Romania and Bulgaria next year.
Mr Cameron said the huge number coming from Poland since it joined the EU in 2004 - put at 1.1 million - was due to Britain putting no controls on immigration. He said: "When a country joins the European Union you can put in place transitional controls. You can say to that country, 'You can't all come here for the first seven years'.
"The last government, when Poland and a lot of other countries joined, didn't put those controls in place.
"Because other European countries did, we did have an enormous influx of people from Poland and those other countries. This time, because the transitional controls have been put in, we are not lifting the restrictions on Romania and Bulgaria alone, it's happening across Europe.
"So I don't think we'll have anything like the situation we had in the Polish situation."