Jemima Lewis: Let us move out of our different-coloured bubbles

The racial fault lines in British society, though less visible than in America, do exist and, are getting wider

For those who love to see America's flaws laid bare, the anniversary, this week, of Martin Luther King's "I have a dream" speech is bursting with potential. Forty years after the great man implored all Americans to "transform the jangling discords of our nation into a beautiful symphony of brotherhood", the civil rights argument has been comprehensively won - yet the dream is still a long way from fruition.

Thousands of campaigners marched on Washington this weekend to commemorate Dr King's speech, but also to deplore the slow pace of practical change.

Depressing statistics were bandied about. Black American men still earn only 60 cents to the dollar earned by white men. Roughly a sixth of African-American men are current or former prisoners - compared with one in 38 whites. New figures from the US justice department suggest that, if current trends continue, black men born in the US in 2001 will have a one in three chance of going to jail during their lifetime. As King's son, Martin Luther King III, told the troops this weekend. "We have a lot of work to do ... to heal the festering sores of racial oppression."

Tempting though it always is to feel superior to our American cousins, race is one subject on which we British should desist from smugness. Although, for historical reasons, the racial fault lines in British society have tended to be less visible than in America, they exist nonetheless - and if anything, they're getting wider.

In an unusually honest and entertaining BBC documentary last week, the journalist Adrian Chiles set out to discover why he - a nice, liberal-minded, middle class chap living in multicultural west London - didn't have any black friends. He went all over the country in search of answers, interviewing Britons of Asian, African and Anglo-Saxon extraction, and discovered the depressingly obvious: that people of every race gravitate towards their own kind.

To the multicultural purist, this instinctive tribalism isn't necessarily a problem - let us live side by side in our different-coloured bubbles, as long as we all respect each other's space - but it's no match for Martin Luther King's vision of perfect racial harmony. In the long term, too, it's no way to run a country. A nation of cliques, suspended in a state of mutual incomprehension, is surely headed for strife.

Americans, being a more dynamic bunch, are at least trying to find ways to batter down the racial barricades. A black bishop in the Deep South recently offered to pay $5 to any white person willing to come and worship with his all-black congregation.

"In church you see segregation, and God is not pleased with it," explained Bishop Fred Caldwell. "This is not just a good idea, baby - it's a God idea." In the event, only a handful of nervous whites took up his offer - but those who did declared themselves thrilled by the experience. "I have always wanted to go to a black church, but I was afraid of being the only white," said one. "I really enjoyed it. I'll be back."

In Boston - a city where blacks and whites have proved especially reluctant to mingle - a man named Reggie Cummings is attempting something similar. A well-to-do software developer, he grew tired of being the only black face in Boston's upmarket nightspots. So he started recruiting other black professionals, via the internet, to help him stage "friendly takeovers" of white enclaves. At his order, hundreds of black people will suddenly stream into a downtown bar, radically transforming its racial make-up. Some of the white patrons flee in terror, but others stay put and do their bit for integration. "It's about time the social scene in Boston became a little more balanced," says Mr Cummings, "if only one place at a time."

A little more balance is what we need, too. Mr Cummings's plan would be more difficult to implement in Britain, where discussions of race often amount to little more than an embarrassed cough, and where the iron grip of the class system further conspires to keep the tribes apart. The public schools - which even now have a near-monopoly on producing tomorrow's bigwigs - are dazzlingly white. So are the middle-class professions: journalism, law, academia, banking. It is extremely hard to break into the British middle class - and almost as hard to break out. A nice white liberal like me can easily move through life without getting to know anyone outside her tribe.

Segregation, whether it's a result of the law or the human psyche, can never be a desirable state of affairs. Martin Luther King may have been addressing America when he called on "all of God's children, black men and white" to mix it up, but his message was global. As he put it: "Their [our white brothers'] destiny is tied up with our destiny and their freedom is inextricably bound to our freedom.

"We cannot walk alone."