Surgeons operate on twins Jodie and Mary

Siamese twins: Despite a fight that went to the High Court and a last-minute protest, 20 doctors and nurses yesterday undertook surgery of sacrifice

One of the most controversial decisions in medico-legal history was put into effect yesterday as surgeons undertook the delicate task of separating the Siamese twins known as Jodie and Mary.

One of the most controversial decisions in medico-legal history was put into effect yesterday as surgeons undertook the delicate task of separating the Siamese twins known as Jodie and Mary.

Under the eyes of the world, 20 doctors and nurses began the surgery that involved sacrificing one child to save the other, at St Mary's Hospital in Manchester. The complex operation, performed in stages by an array of specialists, was scheduled to last 15 hours.

The decision to operate followed a final attempt by opponents of the surgery to have the case taken to the House of Lords. On Friday, the High Court, and subsequently the Court of Appeal, rejected an application by the Pro-Life Alliance to replace the Official Solicitor, Lawrence Oates, as Mary's legal guardian.

Mr Oates had refused to take the case to the Lords even though an operation meant certain death for Mary, after the parents of the twins, who had been opposed to the surgery, declined to do so.

That paved the way for yesterday's operation, which is being done as surgeons had planned, three months after the babies were born on 8 August. Their parents, Roman Catholics from the Maltese island of Gozo, had opposed the operation on religious grounds.

Although there were fears early on that Mary was growing at the expense of Jodie, those fears receded. Doctors judged three months to be the optimum time to allow Jodie to gain strength to withstand the surgery following their traumatic birth. A brief statement from St Mary's yesterday confirmed the operation had begun and said no further information would be issued before today. "At this time our thoughts are with the parents and the surgical team," it said.

The case, which has divided experts in medical ethics and the law, has made headlines around the world, adding to the pressure faced by the surgical team. Led by the neonatal surgeons Alan Dickson and Adrian Bianchi, the team has to demonstrate it is up to the job.

Last month, Professor Lewis Spitz, Britain's leading specialist on Siamese twins who has cared for 17 pairs since 1984, wrote to the Department of Health suggesting Great Ormond Street should become the sole designated centre for the operations. Professor Spitz said yesterday: "With one or less separations taking place a year it is surely better to come into the centre with the greatest expertise."

He added: "It makes complete sense. We are designating centres everywhere for specialist conditions to concentrate expertise, and this is one of the most specialist."

St Mary's is believed to have attempted the separation of only two sets of twins. Mr Dickson, who led yesterday's operation, was involved in the successful separation of a third set, Aoife and Niamh McDonnel, who were born at St Mary's in 1997 and referred to Great Ormond Street. That operation, led by Professor Spitz, was successful but he has not been consulted about the case of Jodie and Mary.

The operation on Jodie and Mary continued to attract criticism yesterday. The Maltese Paediatric Association was reported to have issued a last-minute appeal to its British colleagues saying the surgery violated common practice that parents of severely disabled babies were given the final say over treatment. "In this case the parents have clearly expressed the wish that nature be left to take its course," it said.

The Pro-Life Alliance condemned the decision to allow the operation without it being tested by the House of Lords. A spokesman said: "The right to exhaust all legal defence avenues would not be withheld from a criminal on Death Row anywhere in the democratic world, but has been withheld in the courts of Great Britain from an innocent child. This tragic case is justifiably causing great distress to disability groups in this country and worldwide." However, the High Court ruled that the Official Solicitor had acted with "total propriety" in refusing to take the case to the Lords.

One unanswered question is why the parents, initially so strongly opposed to the operation, chose not to pursue the case to the Lords after being defeated in the Court of Appeal. Lawyers have suggested that after three months in constant contact with the twins they may have developed a bond with Jodie while becoming resigned to Mary's death if it can help her sister survive.

They are reported to have agreed a deal with Granada TV to appear on Tonight with Trevor McDonald, and to be planning to put money they are paid for their interview into a trust to pay for Jodie's future medical care.