A depressed police officer today admitted killing his wife who was having an affair with a man almost half his age.

Pc Graham Jones, better known as Ivor, pleaded guilty to the manslaughter of his 36-year-old wife Maria, on the grounds of diminished responsibility.

He stabbed her to death at their £250,000 detached home in Barwick Close, Ingelby Barwick, Stockton, Teesside on December 2 last year.

Few details about the case were heard at Teesside Crown Court today after the officer, wearing a dark suit, white shirt and black tie entered his guilty plea.

At a hearing at Teesside Magistrates' Court in December, the troubled family background was revealed.

His wife, a hairdresser, supported him through the death of his father and brother which happened within months of each other and Mr Jones began treatment for depression in September last year. The couple were also put through the trauma of a ''malicious'' charge that they had physically abused a child - the case was only dropped on the day the crown court trial was to begin, the magistrates were told.

But the difficulties put a strain on the marriage and Mrs Jones went to stay with her parents in a village outside Burton-on-Trent, the court heard.

Craig Beer, representing the officer then, said: ''Whilst there she formed a relationship with a 21-year-old.''

Mr Jones, 40, was suspicious and when he challenged his wife, she admitted the affair, Mr Beer told the earlier hearing.

''She used to taunt Mr Jones about his sexual powers compared to the 21-year-old,'' Mr Beer said.

The officer, who worked in Hartlepool for Cleveland Police and had 20 years experience, was prepared to forgive his wife, Mr Beer said, but she wanted an ''open marriage''.

At today's crown court hearing, Franz Muller QC, prosecuting, said Mr Jones claimed his wife told him: ''You know I have slept with this man on a number of occasions, how are you going to put up with the fact that I am going to sleep with other people?'' Mr Jones had telephoned his sister Debbie Robertson before the attack.

The prosecution claim she told police officers that he had threatened to kill his wife.

She claimed she told the officers her brother had merely said he wanted to kill himself.

She went to the house and found her brother with a ''haunted look'', magistrates heard.

She called police and they discovered Mrs Jones with multiple stab wounds in the bedroom. She was dead at the scene.

Mr Jones was slumped across her, having taken a number of sleeping tablets.

After he was arrested he told officers he would make further attempts to kill himself.

Mr Jones was remanded in custody and will be sentenced by Judge Peter Fox on June 3. .