Once again, Trevor Phillips has set out to puncture complacency about Britain’s progress as a “multicultural” society. Last night the Chairman of the Commission for Racial Equality (CRE) warned of “walls going up” around some ethnic communities, particularly those of Bangladeshi and Pakistani heritage. This was a thoughtful and well-timed intervention, which did not deserve an intemperate response from the Muslim Council of Britain — a response that suggests that the “race relations busybodies” referred to by Mr Phillips are alive and well, but perhaps no longer at the CRE.

Mr Phillips listed four ways in which tolerance of diversity has been allowed to harden into the effective isolation of communities: evangelical African churches purging children of “evil spirits”; Sikh activists forcing the closure of the play Bekhti; what he calls a “casual acceptance” that the majority of African-Caribbean children grow up without a father figure; and white parents withdrawing children from ethnically mixed schools. On every count, he is right. In that context, his warning that we are in danger of becoming more divided by race and religion deserves to be taken seriously.

On the one hand, it was ever thus. Successive migrant groups have tended to cluster together on first arriving in this country but many, such as Indians and African-Caribbeans, have then successfully made the transition to wealthier, leafier, more integrated enclaves. London in particular is in many ways an extraordinary success story, a city where a quarter of its inhabitants were born abroad and where a flourishing economy is both a magnet for migrants and an engine for their assimilation.

On the other hand, such social mobility is clearly more challenging outside the M25. Mr Phillips claims that about 13 per cent of people of Bangladeshi and Pakistani origin in Leicester and Bradford now live in ghettos. And he suggests that young people of many races are more likely to mix exclusively with their own race than their parents were, partly because schools are becoming more segregated than the neighbourhoods they are in. He does not blame faith schools, but “ semi-voluntary segregation” in mainstream schools and “colour-coded universities”. If such segregation is really widespread, it is a stab to the very heart of middle-class society. It would be useful to see more hard facts from Britain: many of Mr Phillips’s statistics were drawn from America. But if integration has stalled or reversed, that is of concern to all in society.

Mr Phillips may not have all the answers — his speech was light on recommendations. But he has laid down some useful markers: that there should be a national understanding of what ethnic mix is desirable in schools and what undesirable, and that immigrants be able to participate in national life. In that, he is in tune with many of the ideas coming out of the Muslim task forces set up by the Home Office. He is helping to create a climate in which the problems can be discussed; in that, he has already achieved more than many of his predecessors.