The idea that a four-year-old boy killed himself through self-harming was inconceivable, a court heard.

John Smith, according to the defence, hurled himself against a radiator or floor, bruising his forehead, scalp, cheek and jaw and causing a fatal brain haemorrhage.

But Camden Pratt, summing up the prosecution, said the proposition was "wholly unreal", especially since the boy afterwards climbed back into bed to cuddle his dinosaur toy.

His adoptive mother, Michelle McWilliam, found John in bed and called an ambulance.

She and her husband Simon concocted a story that John self-abused to cover up the abuse one or both of them were inflicting, he said.

Mr Pratt told Lewes Crown Court yesterday the boy had 54 bruises and adult bite marks on his body and said the defence case was not believable.

He said there was no history of self-harm, psychological disturbance or autism: "He was a bubbly, affectionate, outward-going little boy."

Mr Pratt said there was a stark absence of independent witnesses to the acts of self-abuse.

No teachers at his school, no social workers who visited the McWilliam home, or even Michelle's mother who visited said they saw such acts.

He said John told visitors he hurt himself but experts had said children of his age would often not tell the truth, especially in front of guardians.

He said John was never taken to a place of safety to be questions by independent people.

Unfortunately, Mr Pratt said, professionals missed what was going on.

He said no experts called to testify had ever come across a child so young who self-abused, who bit his own leg and who pulled his penis so hard that it caused a cut.

Mr Pratt said it was "quite inconceivable" and he urged the jury to return guilty verdicts.

The McWilliams, of Gardner Road, Fishersgate, Southwick, deny cruelty.

The trial continues.