A teacher found bludgeoned to death had begun an affair with a work colleague after they joined a school band, a jury has been told.

Jillian Parnham, 38, began an affair with fellow maths teacher Chris Worth after they joined the band, formed to play in the pantomime at Millais girls' school, Horsham.

Mrs Parnham was found dead at her home in Millmead, Ashington, near Storrington, in March last year.

The prosecution at Lewes Crown Court claims her husband Mark, 36 - an IT teacher at the school - beat her with an iron bar, then told police she was attacked in a violent burglary.

Parnham denies murdering his wife.

At the start of the trial yesterday, Mr Worth, who lives in Chichester, told the court how he and Jillian began their affair in January 2001.

They joined the pantomime band, both playing guitar.

Michael Wood QC, defending, said: "You enjoyed being with her but knew she was married with two children. The relationship developed and became more intimate in February.

"Certainly in these stages she was very anxious to make sure the relationship did not come out."

Mr Worth agreed Jillian regarded her husband as a "third child" who was just in the "wrong place at the wrong time" when they met.

The court heard Jillian would telephone Mr Worth at his homes in Chichester or Horsham and he would immediately call her back.

Parnham became suspicious one day in January last year and dialled 1471 to trace the caller. He then called Mr Worth.

Mr Wood told Mr Worth: "It came as a bit of a surprise to you. You had a rather bizarre conversation about a sweater you had left at their house, which he brought to the school the next day.

"On a couple of occasions when Mark came to pick up his wife, you and she had been alone in her room at the school."

Mr Worth told the court they had been discussing music for the band and practising guitar. He said: "I did not encourage her. She was enjoying it."

Mr Worth agreed he and Jillian had songs they both liked. He made Jillian a tape of love songs and told how she had given him a teddy bear on St Valentine's Day.

Asked if Jillian had planned to tell her husband of the affair, Mr Worth said: "She was getting close to it. If Mark had provoked her enough she would have said it."

The court was told that on the night of her death a row had broken out between Parnham and Jillian and she admitted the affair.

According to Mr Wood, Parnham was under a lot of pressure at the beginning of March because of an Ofsted inspection at the school.

He was also planning a big celebration for their 12th wedding anniversary at the end of the month.

Mr Worth told the court about a phone call Jillian made to him just before 2am on February 15. The following day he and Jillian slept together for the first time.

They slept together again a few days later while Parnham was looking after their two young boys. By March Jillian was taking the contraceptive pill.

Mr Worth told the court that, on the day of Jillian's death, he had seen her at school and they had been to band practice in the evening.

Mr Worth said Jillian was going to go home that night and tell Parnham she wanted to go to a concert.

He said Parnham had never confronted him about the affair and Jillian never said whether her husband had asked her about it.

Former Millais teacher Rebecca Nicholson, whose husband Andrew also played in the school band, said she was at the family home on the evening Jillian died.

She said she waited with Parnham while her husband and Jillian returned from band practice, which they had left at about 7.30pm.

She said she could not detect any bad atmosphere between the Parnhams and described them as "touchy-feely".

The court later heard a tape recording of the 999 call Parnham made on the night Jillian died.

He could be heard saying: "We have been attacked. Somebody burst into our house. Oh my God - I don't think she's breathing.

"It's my wife. What have they done to her head? Oh my God - there's so much blood. Oh Jeez, her head ... there's so much blood everywhere. They have smashed her head in."

Millais assistant head Shirley Mitchell told the jury Jillian had never given her any indication she was having an affair.

She said: "I had no idea, it was a complete surprise. "

She said she had been close friends with the Parnhams for about 15 years.

She described Jillian as "the more dominant partner in the relationship" but said she had never seen Parnham get angry or react violently in any way.

She described Parnham as an excellent teacher.

Under cross-examination by defence barrister Michael Wood QC she said: "The girls adored him. They loved him."

The case continues.