A Southampton man who mentally and physically tortured his partner for two hours before stabbing her to death was today jailed for life.

Judge Keith Cutler told Steven Waters at Winchester Crown Court that he must serve at least 18 years before being eligible for parole.

A trial heard how Waters, 55, had inflicted 15 stab wounds on Anita Bawtree, 34, at their flat in Paynes Road, Freemantle, Southampton in the early hours of April 19 last year.

Sentencing, the judge said Miss Bawtree was a vulnerable woman recovering from mental illness and that Waters was in a position of trust.

The trial heard that he was a cannabis user and was suffering a drug induced mental disorder.

Waters denied murder but admitted manslaughter on the grounds of diminished responsibility. But yesterday, Tuesday, the jury unanimously decided he was guilty of murder.

The judge said: “You subjected your partner to a most terrifying and violent ordeal. I feel it must have been two hours of mental and physical torture that she was ill-equipped to endure. She died at the hands of a man she loved and to whom she looked for for love and protection.”

Anthony Davies QC, mitigating, said: “He has shown deep remorse and regret for all the events of that night and in particular killing the one person he so deeply loved.”

Waters showed no emotion as he was led away.

Waters denied murder but admitted manslaughter on the grounds of diminished responsibility linked to cannabis-induced psychosis.

He told police the drug led him to mistakenly believe his partner was a Nazi on the night he killed her. He also said he thought that he was the victim of a conspiracy by the Government, media and police.

A few weeks before the attack in April last year, he was detained under the Mental Health Act, he told jurors.

He said he collided with the wing mirrors of several other cars while driving, and stopped to speak to the other motorists.

He told them Earth was being attacked by aliens, and he would lead them all to safety, the court heard.

Jurors heard that Waters had battled drink and drugs for many years, and had been admitted to the former Department of Psychiatry in Southampton.

But jurors took less than an hour to decide that he was sane enough to be found guilty of murder.

They had been told how neighbours heard Waters screaming at Ms Bawtree before a “thud” and then silence.

When police arrived there was a three-hour siege as Waters refused to open the door, while admitting he had killed Ms Bawtree. A team of specialist negotiators tried in vain to convince him to give himself up before a team arrived using a Taser to detain him.

After the verdict, Detective Chief Inspector Chris Fitchit said: “It was a difficult case in the sense that here we had two people who had mental health issues.

“There was a partial defence of diminished responsibility which is clearly a difficult area of law for the legal teams and the jury, but we are very satisfied with the verdict.

“Mr Waters’ account was strange to say the least and we were fortunate that we had the assistance of eminent experts in this area who were able to help the jury in coming to their verdict.

As we’ve heard during the trial, Ms Bawtree was a gentle and careful woman who also had mental health issues, and it must be said that this was a tragic case.”