A "girl with a heart of gold" was brutally stabbed to death by a loner with a sexual obsession, a court heard.

Charlotte Flanagan, 22, from Darwen, had lots of friends and was full of life, her mum said.

But the Old Bailey heard that she was killed in her flat above the London pub where she was working after helping locals celebrate last New Year's Eve with a Vicars and Tarts fancy dress party.

The court was told Gareth Richard Horton, 29, of Walmsley Street, Darwen, rang his parents in Lancashire and confessed: "Mum, I've killed Charlotte."

He walked into the River Thames in a failed attempt to commit suicide before being arrested by police who traced his call to a nearby phone box.

The jury was told that 6ft 8ins tall Horton denies murdering Charlotte in her fourth floor flat above the Barley Mow pub in Duke Street, central London.

Simon Dennison, prosecuting, said many of the facts in the case were not in dispute but it was a matter of whether Horton acted with diminished responsibility.

The court heard how Charlotte, died within a minute of being stabbed with a knife by Horton, who used so much force the blade went right through her neck.

He then cut away at the French-maid style outfit she had been wearing, although there was no evidence of any sexual motive, the court was told.

Earlier in the day, Horton had discovered Charlotte, who had previously worked as mentor for young children with the Trinity Partnership in Clitheroe, had begun seeing the step-son of a Barley Mow regular.

Horton heard her talk of spending time with him in Nottingham on New Year's Day.

Mr Dennison added: "His actions show he had an obsession with Charlotte that was both sexual and emotional.

"The thought of Charlotte going out with another man was too much for him."

Horton, the court was told, had moved in with Charlotte as a lodger in May last year after she had begun to struggle to meet mortgage repayments on her home in Walmsley Street, Darwen.

The pair became friends while working in the social services department at Blackburn with Darwen Council. Soon, Mr Dennison said, Charlotte had become the most important person in Horton's life and he relished being friends which such an attractive young woman.

Charlotte, who had gone to work in London for a year before beginning a nursing course, had no such feelings for him, the court was told. After Charlotte moved to London to take a year out from Darwen, Horton began travelling to London to visit her. He had arrived on Christmas Eve and spent Christmas in the capital, the court was told.

But instead of going back home on Boxing Day, he continued to hang around with Charlotte, even though by now he was no longer sleeping on her floor, but at a hotel.

Mr Dennison described Horton as shy and quiet, someone who had lived at home until he moved in with Charlotte and who had never had a girlfriend.

Charlotte's mother, Dorothy Flanagan said her daughter had complained to her about Horton's presence when they spoke on the phone just hours before her death.

"She told me, and these are her words 'He is doing my head in.' "Charlotte then said Horton had spoken about getting a job in London and that she wouldn't be able to stand that."

Mr Dennison said regulars at the pub had found Horton 'difficult' to talk to and that Charlotte had complained to them that Horton had become too 'clingy.'

After Charlotte failed to return from a short break just after midnight, the pub's managers, John and Mary Gordon, allowed Horton to go and see where she was.

He walked up to the fourth floor, picked up a knife on the way up and then stabbed her in the neck. Other injuries included bruising to her legs, a sign of struggling, according to Mr Dennison.

The court was told he left her covered in a duvet before leaving the pub and walking to the River Thames. He rang his parents in Lancashire and confessed to his mother that he had killed Charlotte. He then claimed he was going to kill himself and asked: "Please bury me next to Granny," the court was told.

His mum rang the police in Blackburn, who traced the call to a phonebox near to the Thames. They alerted police in London, and in the meantime Horton spoke to a policeman from Blackburn who had rung the phonebox and confessed to stabbing Charlotte, the court heard.

During his calls home and when speaking to the police, he referred to Charlotte as his girlfriend and said they had had an argument, the court was told.