A teenage Islamic State fanatic was reported by his mother as he plotted an attack on British police officers or soldiers, a court has heard

Muslim convert Matthew King, 19, expressed a desire to kill military personnel as he prepared to stake out a British Army barracks in Stratford, east London.

His plans, which he discussed with an online girlfriend, were thwarted after his mother reported him to the Prevent counter-terrorism programme, the Old Bailey was told.

King, from Wickford in Essex, pleaded guilty in January to preparation of terrorist acts between December 22 2021 and May 17 2022.

On Friday, his mother and siblings attended the start of his sentencing at the Old Bailey.

Judge Mark Lucraft KC said King’s mother had “done exactly the right thing” by contacting Prevent about her son.

Opening the facts of the case, prosecutor Paul Jarvis the court that the investigation into King’s activities “strongly indicates” he has an “entrenched Islamist extremist mindset, holds extreme anti-western views and intended to commit terrorist acts both in the UK and abroad”.

In his early teens, King had “dabbled with drugs” and was expelled from school after becoming aggressive, eventually leaving education at 16.

Around 2020, he became interested in Islam, began to attend mosques and watched Muslim videos on YouTube.

By May 2021, his family noticed he had become more extreme and his mother became concerned he was watching material online promoting hatred, Mr Jarvis said.

He had also developed a friendship with a girl identified only as Miss A, who he met online.

He told her about his jihadist intent, saying: “I just wanna die a martyr.”

When Miss A appeared to support and encourage him, King responded: “I guess jihadi love is powerful. I just want to kill people.”

In further graphic chat, Miss A talked about torturing, mutilating and beheading a soldier and then cutting up the body parts, the court was told.

Meanwhile, King had set up an online account with the retailer Knife Warehouse and bought “tactical gloves” and googles.

Mr Jarvis said: “Mr King’s younger sister told the police that one day her brother had entered her bedroom dressed in combat clothing and goggles. Mr King asked her if she liked his clothes.”

King made videos as he studied potential targets including Stratford Army barracks, police officers outside Stratford Magistrates’ Court and at the railway station.

Some of his reconnaissance videos were overlaid with nasheeds – Islamic chants – and he posted on Snapchat: “Target acquired.”

While planning acts of terrorism in Britain, King had also expressed a desire to travel to Syria to join the so-called Islamic State group.

The teenager sought advice on social media about the best route to cross the border into Syria and searched for IS tactical training videos in the use of knives.

The court heard King had also done web searches for terrorist killers including the Manchester Arena bomber and Jihadi John.

Authorities were alerted after King posted on WhatsApp an image of a male holding a knife with the words: “Those who said that there is no jihad and no battle. They are lying!”

King was arrested by counter-terrorism officers at his home on May 18 last year.

He described his former Islamic name as “Abdul Kalashnikov” and told police: “The only thing which is black and white is the sharia, the law of Allah.”

On being cautioned, he said: “I don’t believe in the UK law, the only law I believe in is the law of Allah.”

After hearing submission by King’s defence barrister Hossein Zahir KC, Judge Lucraft adjourned sentencing until May 26.