Kate Beagley's body was found in woodland in Hertfordshire

Karl Taylor, 27, said Kate Beagley, 32 started prodding herself in the face and neck as they stood in a park where they had been looking at the stars.

Mr Taylor, from Covent Garden, central London, denies murdering Miss Beagley, from Walton-on-Thames, Surrey.

Her body was found in woods at South Oxhey near Watford, Hertfordshire.

Mr Taylor told the court: "I saw her prodding herself and she was moving her head and her neck towards the knife like you would do if you were hysterical."

He said that after she finished, he realised she had died.

She was a very lovely girl inside, but she had a very dark and cold side and I felt it overtook her and overwhelmed her Karl Taylor

"I was crying profusely," he said. "I lay on the grass and looked at the sky."

The couple had been sitting on a bench in Richmond Hill, west London.

Mt Taylor, a former personal trainer, who now works as an unpaid children's football coach, said he did not ring the police because he did not trust them.

He said he picked up the body and carried it to her car because "it was part of her".

'Missed mother'

Taylor said he met Miss Beagley at a West End nightclub and they exchanged numbers.

After arranging to meet, he turned up with a knife up his sleeve because he had been feeling suicidal, he said.

He claimed that after the knife fell out, Miss Beagley picked it up and started to hurt herself as she repeated how she missed her mother, who was in hospital.

"I was very startled, very stunned. I didn't know what to do. I just stood there in awe," he said.

"My picture of her was that she was a very lovely girl inside but she had a very dark and cold side and I felt it overtook her and overwhelmed her."

He denied taking Miss Beagley, a British Gas manager, to the beauty spot to harm her.

The prosecution claim Mr Taylor told police he had intended to steal Miss Beagley's VW Golf car and stabbed her during an argument.

He stripped her body and washed it before dumping it in the woods, the jury was told.

Mr Taylor later threw the murder weapon, her clothing and unwanted belongings on the roadside by the M1, it is alleged.

The trial continues.