The parents of a seriously depressed daughter who hanged herself a day after being allowed home from a mental hospital have won a groundbreaking legal battle in the Supreme Court.

The highest court in the land allowed an appeal by Richard and Gillian Rabone, from Bramhall, Stockport, Cheshire, against lower court rulings that the NHS had no "operational duty" under the Human Rights Act to protect the life of their daughter Melanie - a voluntary patient.

Five justices unanimously decided that the Pennine Care NHS Foundation Trust had a duty to take reasonable steps to protect 24-year-old Miss Rabone "from the real and immediate risk of suicide" when she entered Stepping Hill Hospital, Stockport.

Later the mental health charity MIND welcomed the ruling.

Chief executive Paul Farmer said: "Today's judgment recognises that a positive duty is owed towards patients with mental health problems at times when they are most at risk of harm.

"The law now applies whether or not a patient has been formally detained."

Miss Rabone had attempted suicide several times before she was admitted in April 2005.

Her parents had also found a hosepipe and tape secreted in her room before her admission.

She was in the hospital's Warren Ward for eight days before being discharged on home leave on April 19. Although she had appeared 'brighter in mood', she hanged herself in Lyme Park the day after leaving hospital.

In today's lead judgment, Lord Dyson said the duty to take reasonable steps existed even though Miss Rabone was a voluntary patient and had not been ordered to be detained at the hospital.

He said: "By reason of her mental state, she was extremely vulnerable. The trust assumed responsibility for her. She was under its control."

A decision had been taken to allow Miss Rabone two days' home leave from hospital, but because of her mental state it was a decision "no reasonable psychiatric practitioner would have made".

Lord Dyson and the four other justices - Lord Walker, Lady Hale, Lord Brown and Lord Mance - also unanimously agreed that Miss Rabone's parents were entitled to damages for their ordeal and loss under human rights legislation.

The trust has already issued an apology to the couple and paid £7,500 to settle a claim for Miss Rabone's funeral expenses and her "pain and suffering" before she died.

But Lord Dyson said that was not adequate redress and awarded the couple £5,000 each.

Lord Dyson noted that Mr and Mrs Rabone's main purpose in bringing today's proceedings was not to obtain damages for themselves.

However it was "a bad case" of breach of the operational duty to protect the right to life under Article 2 of the European Convention on Human Rights.

The family ties between parents and daughter were "very strong", and Mr and Mrs Rabone had shown "the utmost concern" for Miss Rabone's mental health.

Lord Dyson said: "They had expressed their anxiety to the hospital authorities about the dangers of allowing Melanie to come home on leave for the weekend of April 19-20 2005 and urged them not to allow it.

"The fact that the very risk which they feared and warned the authorities against eventuated must have made the death all the more distressing for them."

Lord Mance observed: "One can only have the greatest sympathy for the agony of parents who suffer the immeasurable tragedy of loss of child by suicide, made even more acute by the knowledge that this was facilitated by avoidable negligence."