A non-resident Indian couple's attempt to have a 'designer baby' to help cure their ill son was blocked when ethical campaigners won a high court challenge.

Pro-life campaigner Josephine Quintavalle won her battle to stop the "ethically objectionable" screening of test tube embryos to provide donor siblis for sick children.

Justice Maurice Kay ruled that the Human Fertilisation and Embryology Authority had no power to permit tissue typing. The technique enables scientists to find out whether an embryo will grow into a child whose tissue will match that of a brother or sister.

The ruling is a severe setback for Raj and Shahana Hashmi, who were given permission in February to use the genetic screening technique.

Their three-year-old son, Zain, suffers from beta thalassaemia, a potential deadly blood disease, which can be cured using stem cells from the umbilical cord of a baby with matching tissue.

To discover whether an embryo will develop into such a baby, one or two cells must be extracted three days after fertilisation. However, no one is allowed to keep or use an embryo without a licence from the Fertility and Embryology Authority.

By law, such licences can be issued only for assisting women to carry children. There was no suggestion that Shahana had any difficulties in conceiving or giving birth.

Justice Kay said he had sympathy for the Hashmis, but the HFEA had overstepped its powers and had not correctly understood the 1990 Human Fertilisation and Embryology Act.

The act, according to the judge, said the authority could grant licences authorising certain treatments "for the purpose of assisting women to carry children".

He said, "I wish to make it clear that I have great sympathy with the family whose tragic circumstances may be said to have given rise to this case, and I respect the sincerity of the views of those who wish to help them."

The 38-year old Shahana, who was due to undergo her third IVF attempt after Christmas, told a newspaper this month: "These people could destroy not just Zain's right to life, but that of hundreds of other children. What gives them the right to interfere in other people's lives?"

Dr Vivienne Nathanson, head of ethics and science at the British Medical Association said: "The BMA considers it was right to approve treatment for Zain Hashmi."