A far-right "ginger extremist" who fantasised about assassinating Prince Charles so his red-haired son Harry might become king one day has been found guilty of plotting a terrorist attack.

Mark Colborne, 37, who felt marginalised due to his ginger hair, compared himself to the Norwegian extremist Anders Behring Breivik and wrote in his notebook of his plans to kill Charles, the heir to the throne.

"I would sacrifice my life for that one shot. Kill Charles and William and Harry become king. Kill the tyrants," he wrote.

"I want them to see my transition from poor red-haired victimised minority that is constantly walked over to a fully transformed military terrorist."

Colborne, who has been dubbed the "ginger extremist" by British tabloids, compared himself to Breivik, who in 2011 killed 77 people in a murderous spree directed at perceived proponents of multiculturalism.

He got information from the Internet about producing viable explosives and had books containing recipes for producing lethal poisons like cyanide.

Colborne was arrested on June 3 last year, after his half-brother discovered chemicals and papers detailing his racial hatred at the family home in Southampton, on the southern English coast.

Judge John Bevan said it was a "very strange" case involving a "very strange person".

In his defence, Colborne dismissed his diary entries as "angry rants" made when he was off medication for depression.

As the eldest son of Queen Elizabeth II, Charles is the heir to the throne. Second in line is his eldest son Prince William, followed by William's two children, Prince George and Princess Charlotte.

Harry, William's ginger-haired younger brother, is fifth in line.

AFP