The man accused of killing Coulsdon lecturer Lynda Casey broke down in tears in court this afternoon and had to be led away to see a doctor.

Peter Ling, 50, of Wallington, sobbed uncontrollably in the dock when the jury at the Old Bailey were told how the 54-year-old found out about his mistress’s other lover.

The court was told that after hitting Mrs Casey repeatedly with a large rock, Mr Ling left his lover for dead in Banstead Woods and went to find her mobile phone which was in her car, in the Rambler’s Rest public house car park, in Chipstead.

Mr Ling admitted to police that he wanted to find proof from the phone that the Sutton College of Learning Adult had been seeing someone else.

He had previously seen emails between Mrs Casey and her lover when she forgot to log off from her Yahoo email account at his house, but Mr Ling wanted further evidence, the court heard.

Under police interview Mr Ling said: “I didn’t want her to die. I just needed to see her phone for myself. I definitely didn’t think I had killed her.

“I thought she might be seriously injured but I would be able to call an ambulance when I came back.

“I moved her behind a log so no one could see her. Then I walked back to the car.”

But when he found her mobile phone, he discovered dozens of intimate texts and images sent between Mrs Casey and her other lover Ian Tolfrey.

He said: “I found graphic sexual images of her making love to another person. It destroyed everything, I’d given her my heart and she had torn it out.

“I couldn’t imagine anything worse. I didn’t know if it was this Ian or Tolfrey from the emails.

“I didn’t mean anything to her, it was all pretense. I saw all these images and they went back two years.

“She told me she hadn’t been with anyone since she got married to her husband. “ The 50-year-old went back to the woods but could not find Mrs Casey.

He said: “I could have called an ambulance but she had trashed my heart, ruined my world.

“My life was ruined and so was her family's. I walked back to my van and just drove off, I didn’t care any more.

“I didn’t know if she was dead or alive but, because of the images I had seen, I didn’t have any conscience.

Mr Ling was then asked how the argument that led to her death had started.

He told police under interview that he had threatened “to do something stupid” before convincing Mrs Casey to meet him in Banstead Woods.

Mrs Casey apparently interpreted this to mean that Mr Ling would tell her other lover of his existence so agreed to meet him, the jury was told.

Once in the woods, Mr Ling accused Mrs Casey of seeing anyone else but she denied the allegation.

The couple then had a “heated argument” before having sex in the woods.

However, after this Mr Ling refused to let her redress so she had to answer his questions and was unable to run away.

A struggle ensued and it was at this point that Mr Ling picked up the rock and struck the fatal blows, although he admitted she was still “making noises” when he left her, the court heard.

He said: “She carried on struggling but I did it (hit her) again and again. There was a lot of blood. She was gasping trying to catch her breathe.”

The trial continues.