A police officer arrested on suspicion of murder after his 11-year-old son died from a stab wound will not be prosecuted over the boy's death.

Schoolboy Conor Johnson died from a single wound to the heart with a kitchen knife at his father's home in what has now been described as a "tragic and freak incident".

Police confirmed that the boy and his police officer father were alone in the kitchen when Conor received the fatal wound.

Detectives investigated the case on the basis that it could have been manslaughter due to gross negligence by the father.

However, the Crown Prosecution Service yesterday revealed it believed there was "insufficient evidence" to prosecute Mr Johnson.

At the time of Conor's death there were reports that his death had occurred during the course of a bungled martial arts session.

But yesterday police said there was no evidence of such an encounter and would only refer to the incident as being a "freak incident" in the kitchen. Ian Johnson, 39, a police constable for Sussex Police, was arrested following the tragedy in Littlehampton on suspicion of murder.

Yesterday he refused to discuss the case, telling reporters through an intercom system at his flat in Littlehampton: "I have got nothing to say."

Mr Johnson was separated from his wife Sharon, a nurse, before the death of their son.

The case has now been handed over to the West Sussex coroner and an inquest will be held sometime in the new year. Conor was rushed to Worthing Hospital, in West Sussex, shortly after the incident in August but later died from his injuries.

PC Johnson was questioned by officers and was so affected by his son's death that he was bailed to a psychiatric hospital while officers investigated.

A Sussex Police spokeswoman said: "In respect of the investigation into the death of Conor Johnson, formal advice from the Crown Prosecution Service is that there should be no further action in respect of criminal proceedings being taken. The circumstances surrounding the death are now a matter for the coroner."

A Crown Prosecution Service spokesman added: "I can confirm that there was insufficient evidence to pursue for any possible criminal offence."

Det Chief Insp Adam Hibbert, who led the police investigation codenamed Operation Tennis, said: "All the issues were considered in the case, including recklessness.

"The CPS have put their evidential tests to it and they say there is insufficient evidence. There is no suggestion that any martial arts were being used."

Family liaison officer DC Clinton Novelle read a statement from Conor's family at the time of his death in which they said: "Conor's death was like losing a limb.

"He was part of us that can never be replaced or forgotten. He would often help and offer assistance to those in need and give reassurance to those around him.

"Whenever he faced a challenge he would show strength, determination and bravery that belied his youth."