Teacher Mark Parnham broke down as he told a murder trial how he discovered his wife was sleeping with a colleague.

Parnham found contraceptive pills in his wife Jillian's handbag, confirming that she had been conducting an affair with a maths teacher at Millais girls' school, Horsham, where all three worked.

Parnham sobbed uncontrollably as he went on to tell the court how he struck his 38-year-old wife in the head with a metal bar in the lounge of the couple's detached home in Millmead, Ashington, near Storrington, until she was dead.

Parnham, who denies murder, said he confronted his wife, a maths teacher, on March 5 last year about the affair he had suspected for weeks.

The 37-year-old father-of-two told Lewes Crown Court of the moment he found the pills.

Members of the jury also wept as he said: "I felt like screaming. You knew it was the point you had been betrayed, you knew something had gone a lot further. She had lied to me all this time.

"It was devastating. I was angry but then felt as though my heart had been ripped out."

Graphics teacher Parnham - said by friends to be devoted to his wife, whom he met in 1987 when he started work at the school - told the court he decided to tell Mrs Parnham that he knew all about her affair with colleague Christopher Worth.

The pair had become friendly while playing in a school band. Mrs Parnham had started meeting Mr Worth in the evenings on a regular basis, claiming they were going out to watch pub bands.

The court heard how the defendant and his wife began arguing while looking at photos of a previous family summer.

Parnham said: "I said to her, 'That was when you still loved me'. She said, 'You are jealous'. I got really annoyed.

"I said, 'I have seen the pills'. I said, 'How could you do this to me, and the children?'.

"I said, 'You are a slag, you cannot sleep around with someone'."

Parnham then told how he threatened to divorce his wife, saying he would fight her for the couple's two children David, four at the time, and Alex, then 16 months old.

The defendant then claimed his wife attacked him with a metal bar he had brought home from school to learn more about metalwork.

Parnham fought back, and hit her with bar after wrestling it from her.

He said: "She then said to me, 'Now I can say you are a wife batterer. You will never have the children. Chris and I will have them'."

According to the defendant, Mrs Parnham then claimed songs she had played with Mr Worth, including Thorn In My Side by the Eurythmics, were about Parnham, and how Baby Now You're Gone by Bryan Adams was her love song with Mr Worth.

Parnham claimed she said: "I only started playing the piano to escape into his world of music. He was a Scorpio, a real man. You are a pathetic boy."

The court then heard how Parnham "lost it" after his wife attacked him again with the bar as he went to call for an ambulance. He disarmed her and used the bar to hit her around the head.

Still in tears, he told the court: "I just went mad. I had gone mad. I just started hitting her and hitting her and hitting her. I saw blood on the carpet.

"I thought I had hit her hundreds of times. I couldn't believe what I had done. I took my jumper off and put it under her head. I listened to see if she was breathing. I knew she was dead."

Nottingham-born Parnham then ransacked the lounge and went on to claim burglars had broken in and attacked him and his wife - a lie he was later to abandon when questioned by police.

Earlier the court heard how Mrs Parnham claimed he was "paranoid" about her and Mr Worth, saying he ought to see a psychiatrist.

He said he at first accepted her explanation about the time she was spending with Mr Worth, and even bought her flowers and CDs to make up with her.