Almost two-thirds of people in Britain fear race relations are so poor tensions are likely to spill over into violence, a BBC poll has suggested.
Of the 1,000 people asked, 60% said the UK had too many immigrants and half wanted foreigners encouraged to leave.
But the proportion of people describing themselves as "racially prejudiced" was down to 20%, compared with 24% in 2005.
Equality and Human Rights Commission head Trevor Phillips said the findings were "alarming".
Britain's last serious race riots - when violent clashes erupted between white and Asian youths in northern England - happened seven years ago.
Despite this, the poll, carried out by Mori, found three out of four people thought there was now a great deal or a fair amount of tension between races and nationalities.
And almost two in three feared tension was certain or likely to lead to violence, although it is not clear whether people are imagining full-blown street riots or minor scuffles.
Mr Phillips told BBC News: "What worries me is if that friction starts to catch fire - if people do genuinely believe it's going to catch fire then we're in trouble.
"This finding may reflect not what is happening today but the story that's been told of the last 40 years - that if you get people of different kinds together then eventually there's going to be trouble."
The survey was commissioned to mark the 40th anniversary of Enoch Powell's infamous "rivers of blood" speech, in which he described the indigenous population's "sense of alarm and resentment" over immigration.
Speaking of his foreboding, he said: "Like the Roman, I seem to see the river Tiber foaming with blood."
BBC home editor Mark Easton says Powell's words, spoken to a small gathering in Birmingham's Midland hotel, still echo down the decades.
He says the effect of Powell's speech was in fact to force the issue of immigration off the political agenda, with any politician who ventured to broach the subject risking being accused of playing the race card.
This situation still exists 40 years later, our correspondent says.
Five months ago, a Tory candidate in Birmingham, Nigel Hastilow, was forced to step down by David Cameron for saying Powell was right that uncontrolled immigration would change Britain irrevocably.
However, the BBC poll finds many people share that view.
Asked if they thought immigration meant their local area didn't feel like Britain any more, a quarter of the sample agreed - double the amount who felt this three years ago.
Six out of 10 said immigration had made parts of Britain feel like a foreign country.
When Tory leader Michael Howard suggested communities couldn't cope with the pace of immigration during the 2005 general election campaign, he was accused of racism.
However, our correspondent says immigration is now back on the political agenda.
He says: "One reason politicians can debate it again, perhaps, is that the latest wave of immigration is different.
"The million Eastern Europeans who've come to the UK in the last three or four years are not looking to settle for good. Their motives are economic. And perhaps most importantly they are white.
"Forty years after Enoch Powell, the issues of race and immigration have been separated once more."
Immigration Minister Liam Byrne said the government knew immigration was a top concern among voters.
He said: "That is why 2008 sees the biggest shake-up to immigration and border security in 45 years, with a points system like the one in Australia and new rules to make people earn their stay in the UK, including speaking English and abiding by our rules.
"That is what is going to make our immigration system fit for the future."
Source: British Social Attitudes Survey. Years with 99 boxes instead of 100 are where figures did not round to 100%
For the BBC/Ipsos MORI poll results were based on a nationally representative sample of 1,000 GB adults aged 18+ years. Interviews were conducted by telephone using Random Digit Dialling. Fieldwork was conducted on 11-13 April, 2008.