Campaigners for the boy and the white woman had hoped the Attorney General, Sir Nicholas Lyell, would let him stay while appeals were made to the European Commission on Human Rights in Strasbourg.
But, in an unprecedented move, the Attorney General rejected a specific request from the President of the Commission, known as a Rule 36 indication, to suspend the order for the boy to leave.
A spokesman for Sir Nicholas said it was the first time the Government had turned down a Rule 36 indication, but this was because it was "unprecedented" for such a request to be made in proceedings involving private parties.
"The British government is not a party to these proceedings. When it is a matter in which the Government is concerned, it is our invariable policy to comply," he said. However, the Commission's decision to intervene in the case showed its deep concern about possible infringement of the boy's and the woman's "family" rights .
The Government's decision, backed by the Court of Appeal, meant that the boy was reunited with his natural mother at the offices of the Official Solicitor in central London. He was due to leave on a flight back to his native Transvaal last night. But when he was put on the plane he became so emotional that he was taken off again and the plane was allowed to leave without him.
The public relations consultant Max Clifford, who has worked without payment for the boy and his foster mother, said the court's decision to send the boy home had left him very distressed: "I saw them the other night and they are both heartbroken by what is happening. He is a very bright young lad. He had a farewell party and one of the girls from his school had a card with a picture of a judge with horns." Mr Clifford added: "As far as I know, the fight will still go on to let him live here."
The boy, who cannot be named while in this country, was brought to the UK by the white woman, a British citizen with an Afrikaans background. She wanted him to be adopted as a member of her family and to live with her in Maida Vale, north-west London, and be educated at a leading British school.
His natural mother, who worked as a housekeeper and nanny for the British woman, initially agreed to the adoption but later changed her mind.
Earlier court hearings were told that to get around apartheid laws, the white woman had taken responsibility for the boy when he was an infant so that he could stay in her home, while his mother had her quarters elsewhere.
When the woman decided to come to Britain in 1992, the boy's parents signed a document which gave permission for him to go too. But when his natural mother was later questioned by social workers she said she wanted her son back.
Last week the Law Lords backed an earlier Court of Appeal order to send the boy back to South Africa and said that the boy, who has forgotten how to speak Zulu, would be better off with his natural parents.
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