Hayley Richards was three months pregnant when she was killed

Hugo Quintas, 25, is accused of killing Hayley Richards, 23, at her flat in Trowbridge, Wiltshire, last June.

He said: "I lost it when I saw her smiling. I only wanted to hurt her. I... grabbed a knife."

Mr Quintas denies Hayley's murder, but admits her manslaughter on the grounds of provocation.

Speaking through an interpreter, the Portuguese factory worker said Hayley had become upset when he told her he was going to Portugal later that day.

He said she had admitted the affair, and smiled when he became upset.

I was afraid because of the neighbours so I held her mouth with my hand... I told her 'stop please' Hugo Quintas

"She was smiling and I knew that face. I know Hayley. When she has that face she used to provoke me."

He said he had picked up a knife in the kitchen, and gone after her.

"I realised she had opened the door and she was going to run away in the corridor. I held her mouth and cut her throat."

He described how Hayley, who was three months pregnant with his baby, had struggled to get away from him despite her injuries.

"I was afraid because of the neighbours so I held her mouth with my hand... I told her 'stop please'."

Quintas said he later tried to resuscitate her before collecting the knife and other items and driving away from the scene, stopping on his way home to remove his bloodied clothes.

When he got back to his flat he said he confessed to his flatmate Sergio Da Cunha that he had killed Hayley, and claimed Mr Da Cuhna convinced him not to go to the police, saying "Do you want the death penalty?"

Mr Da Cuhna denies one charge of perverting the course of justice.

The case continues.