Revealed: the new evidence that shows Ruth Ellis should never have hanged. Will the judges agree?

The jury took just half an hour to find her guilty after a trial which lasted one day.

Its unanimous decision condemned Ruth Ellis, who had two young children, to the gallows at Holloway prison and made her the last woman to be hanged in Britain, only three weeks after her trial.

But now The Independent has learnt that a new witness has come forward with evidence indicating that one of the most infamous episodes in recent criminal history could have been prevented.

A former nurse living in Australia has said she tipped off the police that Ellis was about to shoot her lover, David Blakely, 26, but they failed to stop the killing.

The witness, Maureen Gleeson, says she spoke to a tearful Ellis shortly before the shooting, and the nightclub hostess told her that she had a gun and was planning to use it on Blakely.

Ms Gleeson immediately contacted the police, but they did nothing to stop the 28-year-old from shooting dead her lover, a racing driver, as he stepped out of the Magdala tavern in Hampstead, on Easter Day 1955.

It is thought that police did go to the pub, but that they did not challenge Ellis. She was hanged on 13 July, 13 weeks after the shooting.

Ms Gleeson's evidence will be heard for the first time tomorrow at the Court of Appeal in London where Ellis's remaining family hope to see her murder conviction reduced to manslaughter.

The family's legal team will argue that Ellis should be acquitted of murder on the ground of provocation - something that was ruled out at her trial by the presiding judge, Sir Cecil Havers.

The evidence will come from a consultant psychiatrist, Gillian Mezey.

Dr Mezey will argue that Ellis was suffering from post-traumatic stress and battered women's syndrome, due to the fact that she was repeatedly beaten and abused by her father and lovers.

Dr Mezey is expected to argue that Ellis's mental state led her to seek out violent partners.

Her torment started at home where as a child she suffered years of sexual abuse from her father, a hard-drinking musician called Arthur Hornby.

Her father also raped Ellis's sister, Muriel Jakubait, now aged 81, who had his child at the age of 15, and has given a sworn statement to her late sister's legal team.

When she was 17, Ellis fell in love with a Canadian soldier and became pregnant. He promised to marry her, but returned to Canada and wrote to say that he already had a wife and four children.

Ellis had a son, Andre, born in September 1944. By the time she was 20, Ellis was working at a West End drinking club as a hostess, and entertaining clients at her flat upstairs.

It was at the club she met a man known as "the mad dentist", George Ellis, an alcoholic who became her husband and who regularly beat her. They had a daughter, Georgina, before the marriage ended.

Ellis became manager of the Little Club, in Knightsbridge, central London, and fell in love with Blakely, a handsome, former public school boy. She became obsessed with him, but he had a string of public affairs which fuelled a burning jealousy.

At the same time, she was having an affair with a client, a wealthy accountant called Desmond Cussen, 34, who wanted to marry her. It was this love triangle that led to Ellis's downfall. She had already had an abortion after getting pregnant by Blakely, but she was pregnant again when her lover punched her in the stomach, leading to a miscarriage.

At the trial, her miscarriage was not revealed. The story of how she got hold of a gun was not told either. It is known that the gun belonged toCussen, who wanted to get rid of Blakely. Her legal team will claim that Cussen talked Ellis into killing him and drove her to the scene of the killing after plying her with alcohol.

Lynne de Maid is heading the legal team bringing the appeal to court. She said that Ms Gleeson came forward three years ago after hearing about the family's attempt to clear Ellis's name.

Ms de Maid said: "Ms Gleeson was walking down the road and saw a blonde lady wearing a mac with something in her pocket and she was crying and really upset.

"She was a nurse and went up to her to ask what was the matter. Ellis told her that Blakely had been treating her really badly. She asked her what she had in her pocket and she said it was a gun. 'I'm going to kill him', she said.

"Ms Gleeson tried to get her to go back to her place for a cup of tea but she wouldn't. So she went to the police station - in Hampstead Heath - and told the officer at the desk and he said that he would send a unit round. She went back to her flat, which she was sharing with two other people, and told them what had happened.

"One of her flatmates later went to the police to find out what happened, but was told that there was no one there when the police arrived.

"When the trial started, Ms Gleeson went back to see the police, but was sent away."

Since providing the testimony Ms Gleeson, who was living in Sydney, has lost contact with the De Maid legal team and her current whereabouts are unknown.

On the night of the killing Blakely had gone to the Magdala with friends to buy cigarettes and beer after an argument with Ellis. As the men emerged, Ellis was waiting with a .38 Smith and Wesson revolver. She called out "David!" and, as he began to run, she fired two shots. After he fell, she fired three more.

She said: "Call the police," and was arrested by an off-duty officer.

The legal team representing Ellis hopes to persuade Lord Justice Kay, Mr Justice Silber and Mr Justice Leveson to reduce the murder conviction to one of manslaughter on the grounds of provocation. If successful, Ellis's remaining relatives could be eligible for financial compensation.

Her son who was 10 when Ellis was hanged, committed suicide in his 20s.

Her daughter, Georgina, a toddler when she was executed, was adopted and died of cancer at the age of 50.

Ms Jakubait, who has led the campaign for an appeal for almost 50 years, and the six grandchildren Ellis never saw, are expected to attend the hearing.

WRONGLY EXECUTED

Derek Bentley

Hanged, aged 19, in 1953 for murder of a policeman. Bentley was convicted on evidence that he encouraged his accomplice, Christopher Craig, then 16, to shoot PC Sydney Miles on a London rooftop by saying,"Let him have it". Pardoned in 1999 on evidence that he had an IQ of 66, suffered epileptic fits and was encouraging Craig to surrender the weapon.

Timothy Evans

Hanged, aged 25, in 1950 for murdering his wife, Beryl, and baby daughter, Geraldine, in a London flat rented from John Christie. Evans said Beryl died during an illegal abortion done by Christie, which Evans fled, leaving the baby with Christie. Christie denied it and Evans was hanged. Christie killed six more women and was hanged in 1953, Evans was pardoned in 1966.

Mahmood Hussein Mattan

Hanged, aged 28, in 1952. Convicted, on the strength of testimony froma witness, Harold Cover, of murdering a shopkeeper by cutting her throat. Pardoned in 1998 after the Crown admitted that Cover - who was convicted in 1969 of slitting his own daughter's throat - was an unreliable witness.

George Kelly

Hanged for the murder of Leonard Thomas in Liverpool in March 1949. A document was found that proved a key prosecution witness, Robert Graham, a convicted criminal, made a statement before the trial implicating another man. The Court of Appeal ruled in June this year that the conviction should be quashed.