David Levin, former chair of the Headmasters' and Headmistresses' Conference of independent schools, recently raised alarm at the way London schools were divided into "ghettos".
Mr Levin, who was raised in South Africa and is head of City of London boys' school, said education should bring together children from different backgrounds, faiths and racial groups.
He gave the example of Stepney Green Maths, Computing and Science College, a boys' school in Tower Hamlets, east London, where 97 per cent of pupils are from a Bangladeshi background.
"A number of those children, through no fault of their own, haven't been outside their council estate, let alone outside Tower Hamlets," Mr Levin said. "This cannot be a good thing."
Government research published in 2006 found that there was some segregation at school level, but when researchers tried to discover whether this segregation was because of the area the school was in, or whether it was due to parental choice, they discovered there was no overall pattern.
Some schools were less segregated than the residential area they served, but some were creating segregation where none existed residentially.
Research from Bristol University published last year found that, although some cities still had deeply segregated schools, segregation nationally was constant or declining.
Percentage of schools where at least 80 per cent of pupils are white British (2007)
74% - Primary
83% - Middle
72% - Secondary
Percentage of schools where a maximum of 20 per cent of pupils are white British (2007)
6% - Primary
5% - Middle
6% - Secondary.