Four-year-old John Smith's adoptive parents, Simon and Michelle McWilliam, denied cruelty in court yesterday and insisted he harmed himself.

Mr McWilliam said the boy, who was covered in 54 bruises and four adult bite marks when he died, was constantly throwing himself down stairs and into furniture.

He said he believed the boy was troubled long before they took him into their home in Gardner Road, Fishersgate, Southwick, and that they were lied to.

He told Lewes Crown Court yesterday he was suspicious John's problems were covered up by social workers and previous foster carers, so he could be "sold" for adoption.

He and his wife, he said, knew nothing about the boy's habit of being sick at meal times until they accepted him into their home.

McWilliam told Lewes Crown Court yesterday how one social worker confided that some colleagues "sold" children to prospective adopters and gave the best possible description of the child's character and demeanour.

He said: "They don't necessarily get the downside (of the child)."

Having lost a child from a previous marriage, McWilliam said he would not have wanted to adopt an unhealthy child.

He said: "I did not want a child who could die."

John died of a brain haemorrhage on Christmas Eve 1999, six months after moving in with the McWilliams.

The boy was described by foster carers and social workers as a gentle little boy, cheerful, polite and with twinkling happy eyes. But he changed and became violent soon after moving in with the McWilliams, the court heard.

McWilliam yesterday admitted he had at times smacked John on the bottom, legs and hand but it was never hard enough to cause injuries.

One bite mark, he said, could have been caused by Michelle when she and John were playing together.

He flatly denied causing any of the four bite injuries.

At one point McWilliam became faint and had to sit with his head between his knees in the witness box after describing John's "horribly upsetting" death.

He blamed social workers, saying they had not done enough to help them cope with John's troubles.

John had two other "mummies and daddies", his birth parents and foster parents, and he became upset that he would be moved on again whenever they visited him, McWilliam said.

The boy poked and pressed his own eyes, pinched skin on his neck, and once suffered a carpet burn that marked skin over one half of his face.

McWilliam said he was shocked when he saw the "horrible" burn but he did not consider it, or any of his bruises, bad enough to seek medical help.

He said the boy's behaviour was bizarre but the couple informed social workers who told them John would settle down.

One facial injury on John was picked out from a photograph taken of the boy's class on Book Day. McWilliam said he did not know how the injury was caused.

The court heard how Mrs McWilliam had reported a tear in John's penis to a foster carer and a teacher and how John admitted causing it himself with scissors.

The foster carer advised he should see a doctor but McWilliam yesterday said that was not the message he received.

He said he understood the carer advised they seek medical help if the injury continued to bleed.

Michelle, he said, cleaned the wound and it stopped bleeding.

Cross examined by Camden Pratt QC, McWilliam admitted he made no mention of the bleeding when he wrote to an adoption panel when the couple were planning to take in another child.

Today McWilliam told how John regularly had bruising. He said he rarely witnessed the injuries but was told of them by his wife.

During November 1999, a month before the boy's death, there was a catalogue of wounds.

McWilliam said his wife told him how the boy had fallen downstairs and on another day how John had deliberately banged himself on a chair, causing a black eye.

The injuries were seen by a social worker who, a few days later, spotted new wounds to the jaw. A social worker said they looked like finger marks where John had been grabbed round the mouth.

McWilliam said he could not recall seeing them, but again stressed that John regularly had injuries on his face.

The trial continues.