The reluctance of some councils to arrange adoptions because of a child's race means the UK faces a collapse in adoption rates, the outgoing chief executive of Barnardo's has warned.
Martin Narey told the Guardian this "prejudice" was so entrenched that it would be difficult to reverse.
He said the adoption rate of babies must "quadruple" in the next few years.
Children's Minister Tim Loughton has said it is unacceptable to deny a child a home because of ethnic differences.
Children from ethnic minorities are over-represented among those seeking adoption, but it typically takes three times as long to place them.
Official figures show that 2,300 children were placed for adoption in 2009, compared with 2,500 the previous year, and down from 3,400 in 2005.
In about 20% of cases identified as suitable for adoption, no placement is found.
Mr Narey, who has run Barnardo's for more than five years, said the numbers of toddlers and older children placed with new families needed to increase dramatically.
The charity's outgoing chief executive, who is being replaced by Anne-Marie Carrie, accused local authorities and adoption agencies of showing a disregard for the law through a reluctance to allow white couples to adopt children from different ethnic backgrounds.
"The law is very clear. A child should not stay in care for an undue length of time while waiting for adoptive parents of the same ethnicity.
"But the reality is that black, Asian and mixed race children wait three times longer than white children," he said.
In November, in a letter to local authorities in England, the children's minister said he was "troubled" to hear that sometimes "there may be over sensitivity on the grounds of ethnicity when it comes to the matching of children with prospective adopters".
He wrote: "It is plainly unacceptable for a child to be denied loving adoptive parents solely on the grounds that the child and prospective adopters do not share the same background.
"The primary consideration must surely be whether the family can offer a strong, safe, stable and loving placement that can meet the child's needs."
And, in a speech last year, the minister also said: "We know that a child tends to do better if adopted by a family that shares their ethnic and cultural heritage.
"Although the law and guidance is clear that due consideration needs to be given to language, religion, culture and ethnicity, this isn't translating into practice.
"It is much better that a child is adopted by loving parents than left waiting for their future to be decided."
BBC News
