'It is clear that the purpose of this proposed attack was to promote the ideology and agenda of Isis'

The teenager, now 15, from Blackburn, Lancashire, was radicalised on the internet by Islamic State propaganda and was said to be determined that police officers would be beheaded at a parade on April 25.

In July, the boy - thought to be Britain's youngest terrorist - pleaded guilty to inciting terrorism overseas.

Outlining the case at the start of a two-day sentencing hearing at Manchester Crown Court, prosecutor Paul Greaney QC said: "In short, from the bedroom of his parents' suburban home the defendant plotted an attack upon an Anzac Day Parade in Melbourne.

"He did so with an alleged Australian jihadist named Sevdet Besim, who we suggest used the online name 'Illyas'. Their plot was developed over the internet and the intention was that police officers should be murdered by beheading.

"It is clear that the purpose of this proposed attack was to promote the ideology and agenda of Isis. A striking feature of the case is that, at the time of the offence, the defendant was aged just 14.

"It is clear that he had been radicalised by Isis propaganda accessed by him over the internet and the evidence establishes that the contact with his Australian collaborator was instigated by a well-known Isis recruiter and propagandist named Abu Khaled al-Cambodi, himself an Australian, who has promoted the idea of terrorist attacks in his homeland.

"There is no doubt that there was a determination on the part of the defendant and Sevdet Besim that the plot should be carried through and the contact between the two included frequent references to the production of a martyrdom video by Besim for al-Cambodi which, no doubt, al-Cambodi intended to use for propaganda purposes.

"In the event, fortunately, the authorities here and in Australia intervened and a plot that would in all probability have resulted in a number of deaths was thwarted."

The prosecutor detailed the background of the Muslim defendant and said that in the period leading up to his offending his family circumstances "appear to have been difficult" when his parents were said to have separated.

From the age of 12 he was "undoubtedly a troubled young person" and was excluded from school on a regular basis for regular abusive and disobedient behaviour, Mr Greaney said.

The youngster, who cannot be named for legal reasons, was said to have "strong religious convictions" and was disruptive when he attended a large secular school where most of the pupils were white.

On one occasion he praised Osama bin Laden and stated his own desire to become a jihadist and a martyr, the court heard.

The defendant was later referred to the Government's counter-extremism programme Channel after his mother explained to the school that he spent all night on his computer studying foreign affairs and "seemed to have the weight of the world on his shoulders".

Mr Greaney said: "She stated also that he spent time talking over the internet to persons that he had not met."

It led to him moving schools but his poor behaviour continued and more exclusions followed, the court was told.

While there he threatened a male teacher on "many occasions" and on one date he said he would "cut his throat and watch him bleed to death".

Another male teacher logged a comment from the youngster that he was plotting to kill someone, the prosecutor said.

The voluntary Channel programme closed his case in July 2014 after the school noted no particular features of radicalisation.

Later that year his behaviour at school escalated and in one lesson he was heard talking to other pupils about beheading, the court heard, and pushed his phone into the face of a teacher, which played a video showing dead and bloody bodies on the floor.

The teenager went on to express extremist views on matters related to Islamic State and terrorism.

Mr Greaney said: "He regularly mentioned death and unpleasant methods of torture. He also spoke of his desire to be a suicide bomber, stating that if he had to choose where to detonate his bomb it would be on a plane in order that he could maximise the fatalities."

In one class he was reported to have said to a teacher: "You are on my beheading list," and said the teacher was now on the list above a colleague.

A second referral to Channel took place in November 2014 but the youngster continued to threaten to kill teachers and told one "your time has come" as he referenced terrorism and beheadings.

In one lesson on the death penalty alongside the comment "killing another person is immoral", he had written: "You could not be more wrong."

Mr Greaney said: "In a meeting with officers from the Channel programme he similarly expressed the view that killing could be justified on religious grounds and to a social worker the same day he described the Charlie Hebdo attackers as his heroes."

By early March this year, said Mr Greaney, "a tipping point" had been reached.

He said: "The teaching staff at the school were increasingly concerned for their own personal safety and the evidence of (the defendant's) radicalisation was overwhelming.

"(The defendant) had disengaged from the Channel process and attempts to divert him from a path of extremism had failed."

The teenager told Channel workers that he knew he was going to be killed or go to jail and he blamed the Channel process for radicalising him after previously saying it had prevented him going to the school of his choice.

Mr Greaney said: "He said that he had a new identity on the internet and was in contact with many adults through that means, something that in the event proved to be quite true."

The boy was arrested at his home on the morning of March 25 on suspicion of making threats to kill, and his phone was examined.

The prosecutor said: "The screensaver for the handset of the Samsung Galaxy was the flag of Isis. The handset also contained a video showing the events immediately preceding a beheading by members of Boko Haram along with photographs of other beheadings, including by Jihadi John, to whom (the defendant) had referred in discussions at school.

"Isis propaganda was found on the handset, including three editions of an Isis magazine, one of which contained excerpts from a speech by an Isis spokesman calling for lone wolf attacks in home countries.

"Footage of an anti-Shia lecture by an extremist preacher was also discovered. There were hundreds of photographs showing Isis fighters, prominent individuals associated with Isis, dead Syrians and other Isis calls to arms."

The prosecutor said: "(The boy) had also used the handset to search for news items relating to Isis and associated issues. In addition, he had searched for information about high explosives and associated topics. In other words, the handset revealed the clearest evidence of (his) mindset and of his religious and political views."

Mr Greaney went through evidence of the boy's social media contact with other extremists around the world.

He said: "And so, putting (the defendant's) behaviour at school together with his activities over the internet, a clear picture emerges of a young person who was, by March 2015, thoroughly and dangerously radicalised and committed to Isis and the idea of violent jihad, and who was, moreover, wired into the Isis network."