The knifeman with a cut-glass accent who launched a random attack on businessman Philip Hey acted with planned determination, a top forensic psychologist suggested last night.

Earlier this week, Mr Hey bravely told the Telegraph & Argus of his horrific ordeal when a polite, smartly dressed teenager knocked at his door in the dark, borrowed a torch and then stabbed him through the throat.

Consultant clinical psychologist Elie Godsi, who carries out character assessments for courts and police, says he believes Mr Hey’s attacker had not carried out such an attack before – but would now find it easier to strike again.

“Someone for whom this type of knife violence is commonplace would have stabbed his victim straightaway,” said Mr Godsi, author of Violence and Society: Making Sense of Madness and Badness.

“There has been a lot of time gone into building up the courage to do this.

“It sounds like the first time. It could be a case of mistaken identity or that the attacker could be unwell and delusional.

“He may have been psychotic and in which case anything could have been going through his mind.

“At that moment he targeted the victim for a reason, which could have been anything – he could even have believed his victim was an alien or anything,” Mr Godsi, who is based in the East Midlands, said.

“The trouble is, having done it once before – it will be easier the next time.”

Asked if he thought the inclusion of a 12-year-old brother in the tale told by the knifeman hinted at multiple personalities, Mr Godsi said he thought that was unlikely.

“It wouldn’t usually play out like that, people tend not to externalise other personalities, they keep those internally,” he said.

Mr Godsi also said when people are in delusional states they do not conform to normal rules. “He would be detached from the world and not feeling in the world as we do,” he said.

Mr Godsi also said the upper-class accent and manners of the knifeman were of little significance if the attacker were mentally unwell.

“My gut feeling is that while in reality this is a random attack on an innocent victim, it was not that way for the attacker,” he said.

“And if this person is very unwell, someone in the psychiatric system or a parent will know who it is. That’s where the police should probably be looking.”