A frenzied drug addict who suffered from paranoid delusions stabbed a 75-year-old stranger to death outside a newsagent's because he believed the man was part of conspiracy to abuse his children, a court heard today.

Stephen Newton, 42, stabbed Philip Hendy in the neck and back as he came out of A and J News in Greenbank Road, Bristol, on the morning of Sunday April 29 last year.

Mr Hendy died in intensive care on May 8.

Bristol Crown Court heard today that Newton was suffering from psychosis fuelled by a long-term addiction to amphetamine.

He believed that there were tunnels under his house from the neighbouring chocolate factory which allowed people to get into his home and abuse his mother.

He also believed that his three children were being sexually abused by the American government which had given his son a sex change to look like Kylie Minogue and that the House of Commons knew about this.

Moments after the attack on Mr Hendy, Newton then followed and punched another 85-year-old man to the ground as he was walking along the street because he too was thought to be involved in the delusion.

Dr Paul Cantrell, consultant forensic psychiatrist who was in charge of Newton's care at a secure mental health unit after his arrest, told the court that Newton had a long history of mental ill-health.

He said Newton had a personality disorder and that his chronic abuse of high doses of amphetamine triggered paranoid delusions.

The first reports of his delusional beliefs came from his ex-partner in 2006.

Dr Cantrell agreed with Richard Smith QC, representing Newton, who said: "You were of a view that these were the set of delusional beliefs that were persisting at the time of the killing and that Stephen Newton's actions were part of those delusional beliefs, that he irrationally concluded that the fatally injured and the injured party were part of that persecution."

Dr Cantrell said: "My formulation of his motivation at the time is that the level of persecution led him to the need to defend himself proactively to end the abuse of his children.

"His mental state, his faculties of reason and motivation behind his actions were absolutely linked and driven by his paranoid psychosis."

Newton admits carrying out the stabbing but denies murder.

The jury is being asked to consider whether he was suffering from an abnormality of the mind at the time which diminished his responsibility for the crime.

The case continues.