A police officer is in a psychiatric hospital after being arrested for the suspected murder of his 11-year-old son.

Detectives said they did not believe PC Ian Johnson, 39, intended to kill his son Conor, described by his family as a "brave and determined" boy.

The youngster died despite emergency surgery for a single stab wound to his heart. It is believed he was stabbed with a household kitchen knife at his father's flat in Norfolk Road, Littlehampton.

Sussex Police said they had not ruled out the possibility that Conor was stabbed during a martial arts "play fight" with his father, who is on bail.

The pair had a keen interest in martial arts and it was believed they may have been practising techniques when the incident happened.

Detective Chief Inspector Adam Hibbert, leading the inquiry, said Mr Johnson had originally been arrested on suspicion of murder, but that "other offences" were being looked at.

He said: "I am treating this as a criminal investigation, until otherwise proven, and can confirm a man has been arrested in connection with this incident and is on bail. The man is Conor's father, who is a serving Sussex Police officer."

Police officers and ambulance paramedics were called to the flat at 10pm on August 13 following a report by Mr Johnson of the stabbing. Conor often spent time at the flat following the amicable separation of his parents.

Surgeons at Worthing Hospital battled in vain to save the youngster's life.

Conor's family paid tribute to the 11-year-old. In a statement they said: "The death of Connor is like losing a limb. He was part of us that never can be replaced or forgotten. He would often help and offer assistance to others in need and give reassurance to all around him.

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

Conor, who recently returned from a two-week outdoor survival course, had just left Georgian Gardens Junior School in Rustington and was looking forward to starting at Littlehampton Community School.

He spent most of his time with his mother Sharon at her Littlehampton home.

Sussex Police said detectives were not looking for anyone else in connection with the death. She added that Mr Johnson had not been suspended from work.