A veterinary nurse, forced to have a Caesarean section against her will, yesterday won the right to sue the hospital which carried out the operation following a landmark court decision.

The Court of Appeal ruled the hospital, a health care trust in south London, and a social worker who organised her detention under the Mental Health Act had all acted unlawfully.

The 30-year-old woman was detained under the Act after a doctor said she was suffering from pre-eclampsia - a condition which threatened her life and that of her unborn baby - but had refused treatment.

But three Court of Appeal judges ruled that they had acted unlawfully and criticised the judge who granted an injunction allowing the hospital to operate.

Campaigners welcomed the decision and said the Mental Health Act had been used inappropriately to force the woman into surgery.

After the hearing, the woman's solicitor, Richard Stein, said: ''We are very pleased with the outcome. The court has supported the position that there is no legal basis for either detaining our client or in forcing her to have a Caesarean section.

''The position is now clear for all medical professionals and social workers in the future that women patients can decide what they want in relation to treatment over their births.

''Our client has asserted from the start that what was done to her was unlawful, and that has now been backed by the courts.''

The woman was detained by Merton Borough Council social worker Louize Collins after her local GP warned that she was refusing treatment for severe pre-eclampsia.

She rejected the advice because she wanted the baby to be born naturally, the court heard.

The nurse was later seen by Miss Collins, who obtained an order under the Mental Health Act after two doctors repeated the advice and she adamantly refused to accept it.

The woman was admitted to Springfield Hospital in south London the same day against her will, and later transferred to St George's Hospital in Tooting, which then made an application in the High Court to dispense with her consent to treatment.

In yesterday's ruling, Lord Justice Judge said: ''Even when his or her own life depends on receiving medical treatment, an adult of sound mind is entitled to refuse it. This reflects the autonomy of each individual and the right of self determination.''

He added: ''How can a forced invasion of a competent adult's body against her will, even for the most laudable of motives - the preservation of life - be ordered without irremediably damaging the principle of self determination?''

Of the use of the Mental Health Act, the judges said: ''The Act cannot be deployed to achieve the detention of an individual against her will merely because her thinking process is unusual, even apparently bizarre and irrational, and contrary to the views of the overwhelming majority of the community at large.''

The three appeal judges also issued a list of guidelines for the medical profession at the end of the ruling because the case had ''highlighted some major problems'' when a woman is in need of a Caesarean operation.

They said that if there was any real doubt about the capacity of the woman to decide, the issue should be decided by the courts.

But if the patient is competent to accept or refuse treatment - which she may be, even if detained in hospital under the Mental Health Act - the hospital is obliged to accept her decision.

Lord Justice Judge will decide on damages for the woman at a further hearing.

The hospitals involved and Merton council are expected to appeal to the House of Lords.

Campaigners backed the court's decision and said it was important in helping clarify what was appropriate intervention.

Grainne McMorrow, legal and policy manager of the mental health charity Sane, said court action seemed an appropriate way to deal with such a controversial issue.

The British Medical Association said the case showed an inappropriate use of the Mental Health Act.

''The BMA supports the view that a pregnant woman who has chosen to take her foetus to term has a special moral obligation to that foetus to act in its best interest and avoid causing it serious harm,'' said a spokeswoman.

''But the fact that she is perceived to have moral obligations does not mean the health professionals or the courts can compel her to fulfil them.''

John Wadham, director of civil liberties campaign group Liberty, said: ''However ill-advised a woman's own decision might seem to a doctor, forcing someone to undergo intrusive surgery against their will can only be justified where the individual is unconscious or completely mentally incapable of making such a decision herself.''

But Jane Ramsay, head of legal services at Merton Council, said: ''We are disappointed at the legal outcome, but we are pleased the judges said they admired our social worker's courage in a life and death situation.''

Conflict of ethics Page 17