A redheaded British white supremacist who plotted to kill Prince Charles with a sniper rifle so Prince Harry could become king has been found guilty of preparing an act of terrorism. Mark Colborne, 37, from Southampton, said he felt "belittled by society" for being ginger and wrote in his diary how he wanted to assassinate the Prince of Wales in order to help the ginger prince become king.

He was also found to have trawled the internet to purchase ingredients for cyanide in order to commit a terrorist attack that would bring "attention our pain – not just mine but my brothers around the world".

Colborne compared himself to Norwegian terrorist Andres Breivik, who murdered 77 people including 69 during a mass shooting in Utoya, in two attacks in 2011.

Colborne was arrested last June after his half-brother found papers detailing plans to "put a bullet" in Prince Charles's head, as well as an assortment of books and manuals with titles such as Assorted Nasties, Silent Death and The Poor Man's James Bond.

During the trial at the Old Bailey, the court heard extracts from his writings. One read: "Wouldn't it be great to have a military silent rifle, take up a good stealth position and put a bullet in Charles' head. I would sacrifice my life for that one shot. Kill Charles and Prince Harry becomes king... Kill the tyrants and become free from tyrannical future rule."

While comparing himself to Brevik, Colborne wrote: "I'm looking for major retribution, a mass terrorist attack which will bring to the attention our pain, not just mine, but my brothers around the world."

He added: "I will put a major dent in England, one that is felt around the world. If for some reason I cannot perform a major operation then I will still opt for low-level attacks."

Colborne has been found guilty of plotting a terror attack "for the Aryan people" after a previous jury was discharged for failing to reach a decision earlier this year. During the original trial, prosecutor Alison Darlow QC told jurors Colborne suffered from depression and led quite an isolated life.

She said: "He clearly had experienced a troubled childhood and perceived himself as marginalised and belittled by society because he was a white, ginger-haired male."

Colborne is due to be sentenced on 3 November.

Investigating officer Det Sgt Andy Hedley said: "It is clear from our investigation that Mark Colborne is a fantasist who had ideas and plans about committing acts that could cause great harm to other people.The 37-year-old went beyond the realms of fantasy when he wrote down his intentions and bought the chemicals that would have enabled him to carry out these plans.

"Fortunately, he didn't ever carry out any of these plans and from all the evidence we found, Colborne had not progressed to actually making poisons or viable devices that would have presented an immediate threat to the community."

He added: "I would like to thank and praise Colborne's family who were brave in coming forward to tell us about concerns they had about his behaviour."