A Stockport couple whose severely depressed daughter hanged herself after being allowed home from hospital have won a six-year legal battle.
The Supreme Court ruled Pennine Care NHS Trust failed to protect Melanie Rabone, 24, a voluntary patient at Stepping Hill Hospital in 2005.
Campaigners welcomed the decision as a ''landmark judgement" for voluntary patients in psychiatric care.
The trust has admitted its failure and apologised to the Rabone family.
Richard and Gillian Rabone, from Bramhall, took their case to the Supreme Court after a judge ruled the NHS had no duty under the Human Rights Act to protect their daughter's life because she had not been detained.
However, the court has now upheld their appeal that, under Article 2 of the European Convention on Human Rights, Miss Rabone should have been accorded the same duty of care as a patient detained under the Mental Health Act.
After the ruling, Mr Rabone said: "It's a relief but it's tinged with sadness that it doesn't help Melanie.
"In all the past judgements, it was never clear whether somebody who was not detained by an authority - be it a prisoner or a hospital patient - was not subject to Article 2 in terms of protecting their life.
"The judgement that has been made today clears that distinction completely away and hopefully, hopefully it will mean hospitals will have to take far more notice in terms of the care... It is irrelevant whether a patient is sectioned or not."
Added Mrs Rabone: "What it's achieved is something that's worthwhile and I know that if Melanie was here she'd be so pleased."
Miss Rabone had a history of depression, the court was told.
On 4 March 2005, she tried to take her own life and was admitted to Stepping Hill where she was diagnosed as suffering from severe depression.
She was discharged having made a recovery but, two weeks later, cut both her wrists with broken glass.
Miss Rabone agreed to an informal admission, prescribed a course of drugs and was kept under observation. A ward nurse assessed Melanie as a moderate to high suicide risk.
Mr Rabone told the hospital his daughter was not improving and that she should not be allowed home.
Despite this, her consultant psychiatrist agreed to allow Miss Rabone home leave for two days on 19 April. The next day, she hanged herself.
The Supreme Court judgement said that, because the decision to allow home leave was "one that no reasonable psychiatric practitioner would have made, the trust failed to do all that could reasonably have been expected to prevent the real and immediate risk of Melanie's suicide."
Full compensation of £7,500 was paid to Miss Rabone's estate in 2009.
A spokesman for the mental health trust - which operates services at Stepping Hill Hospital - acknowledged that it "did not manage Melanie's care as it should have."
The Supreme Court's decision has been welcomed by leading mental health and human rights organisations.
Paul Farmer, chief executive of mental health charity Mind said the judgment recognised a "positive duty is owed towards patients with mental health problems at times when they are most at risk of harm".
Emma Norton, legal officer for the human rights group Liberty, described it as a "landmark human rights judgment" giving voluntary patients in psychiatric care the same legal protection as sectioned patients.
She said "Hospitals rightly acknowledge their serious duties to detained people - why should those who have asked for help be any different?"