The growth in the number of immigrants coming to the UK from eastern Europe has presented "major new issues" for the established population, the head of the Commission for Racial Equality said.
Trevor Phillips said that one reason "we are so anxious" about the recent influx was that the new immigrants were competing for better jobs. He said they brought with them their own institutions and were settling in greater numbers in smaller areas.
Speaking at The Royal Geographical Society, he said: "There are some features of this migration which make it, from the point of view of the average citizen, very different to the post-Empire wave. The first is pretty obvious if you go into any Starbucks, or walk past a building site. These people come to work, and to earn. That doesn't mean that settled folk are pushed out of the labour market. But most of those who come from the EU accession countries are young, often highly educated and, crucially, single and child-free.
"In our last wave of migration, most people came, did the jobs no one else would, and rapidly brought their families to join them. The upside is that this is largely dependent-free migration; but it is socially significant - an influx of young men or young women will change any community."
Mr Phillips said that between July 2004 and March 2006, almost 5,700 accession country nationals registered as bus, lorry and coach drivers. There were more than 11,500 care workers, 1,400 teaching staff, 550 dental practitioners and more than 1,750 GPs, hospital doctors, nurses and specialists.
Mr Phillips warned politicians that their responses to the new immigration must be measured. "Today the UN reckons that some 200 million people live and work outside the country of their birth. In recent weeks, the newspapers and the airwaves have been full of chatter about the potential consequences of the accession of Romania and Bulgaria to the EU. Set that noise against the background of public anxiety about terrorism inspired from abroad but executed at home and you have a recipe for policymaking by panic."
A spokesman for Business for New Europe, representing British business support for further integration, said: "Young people all over Europe are taking advantage of the freedom to live and work anywhere in the EU, and pursuing opportunities outside their country of birth. This is to be welcomed. The immigrants from eastern Europe to the UK have made an immense contribution to the private and public sector in all regions."
Mr Phillips said the migrants arriving in Britain 100 years ago broke with the past, unlike those who can now keep the link alive through travel and communication. "Indeed, we expect that the majority of those coming from the EU accession countries will return home within a few years," he said.
Mr Phillips said the new immigrants were establishing their own places of worship, shops and even media outlets. "There's nothing wrong with these preferences," he said. "But it does present the possibility that the range of areas in which we share experiences as a whole nation is shrinking daily." He said rather than settling in large cities, new migrants were focusing on relatively small towns in large numbers.
Mr Phillips, who said Britain was "sleepwalking to segregation" last year, insisted immigrants were needed to sustain our workforce. But he said: "In this new world of more rapid immigration, coupled with an unprecedented threat to global security, we cannot continue to pretend that there are no costs faced by our changing communities."
Mr Phillips warned that Britain was verging on "unacceptably high" ethnic polarisation in some areas and claimed the education system was encouraging that division. "Separateness tends to encourage inequality of treatment," he said. "Living separately means that different groups of people have their experiences defined by their ethnicity rather than their ambitions. We know that the more we allow people who live here to feel they do not belong to this society the higher the risk of their taking hostile action against it."