Ababy-faced teenage terrorist who was radicalised in his bedroom came within hours of an attack on a Justin Bieber concert, a judge has said.

Lloyd Gunton, 17, who was arrested hours before he intended to commit mass murder in a vehicle attack, was handed a life sentence with a minimum term of 11 years.

A judge allowed his identity to be published for the first time as he was detained.

The teenager, who suffers from an autism spectrum disorder, was convicted of preparing for terrorist acts after a nine-day trial at Birmingham Crown Court last November.

He armed himself with a hammer and knife and wrote a so-called martyrdom letter as part of his plan to attack and kill “non-believers” on the streets of Cardiff.

Gunton, who had conducted “virtual surveillance” of targets, including a Justin Bieber concert at the Principality Stadium, was detained at his home in the Llantrisant area of south Wales on June 30 last year.

Gunton posted threats on social media CREDIT: WALES NEWS SERVICE

Ordering Gunton to be detained at Her Majesty’s pleasure, Judge Mark Wall QC told the former A-level student: “The police found a rucksack in your room which contained a knife, a hammer and what has been referred to as a suicide note or a martyrdom letter.

“In the martyrdom letter you referred to yourself as a ‘Soldier of Isis’.

“The letter was written in such terms that it was obviously to be found and read after you had carried out a terrorist attack.”

The judge described the items found in the rucksack as a “terrorist’s kit” and said it was clear from Instagram posts in English and Arabic that Gunton had planned to launch an attack on June 30.

The judge told the teenager: “I sentence you on the basis that at the time of your arrest you were within hours of committing an act of atrocity on the streets of Cardiff.

“It is clear that Cardiff was your target. In particular you had made a number of online searches in connection with a concert that was being given by Justin Bieber at the stadium in Cardiff on 30th June.

“Whether you would have targeted people attending that concert or others going about their lawful business in Cardiff that night is not certain.

“It is not possible to estimate how many people would have been murdered or seriously injured by your actions, as the attack was foiled before you could undertake it.

“I am sure that you planned not just the killing of one person but rather mass murder.

“In my judgment I must pass an indeterminate sentence. Your actions show a total disregard for human life.

“I cannot foresee a time when I can be confident that your danger will have ended or decreased sufficiently to enable me to pass a determinate or extended sentence.”

Gunton shared chilling pictures on social media CREDIT:  WALES NEWS SERVICE

The teenager was also convicted of two counts of encouraging terrorism by posting extremist material on Instagram, and two charges of possessing Isis propaganda magazines.

At the start of Gunton’s trial it emerged that he had written a note apparently for distribution after his death reading: “I am a soldier of the Islamic State and I have attacked Cardiff today because your government keep on bombing targets in Syria and Iraq.

“There will be more attacks in the future.”

Cardiff’s Castle quarter was among the areas researched by the boy using Google maps, while other searches sought details of a shopping centre, the city’s Central Library and the New Theatre.

Gunton showed no obvious emotion in the dock as he was told that his autism, young age and previous good character had saved him from an even longer minimum term.

The judge told the teenager the “usual range” of minimum sentences for someone convicted of similar offences was 21 to 30 years.

The judge said the would-be Isis attacker, who only held a provisional driving licence, had carried out significant planning.

The judge told Gunton: “You were committed to carrying out the attack throughout a protracted period, a commitment best demonstrated by your martyrdom letter and open support for Isis on Instagram.

“You were dedicated to the cause for approximately one year: this was no passing phase.

“The author (of a pre-sentence report) recognises that at present you are a high risk of re-offending and that if you do, you pose a high risk of causing the public serious harm.”

Turning to the defendants mitigation, the judge said of Gunton’s diagnosis of autism: “This condition made you something of a loner and someone more easily impressed by the things you read on the internet.

“Yours is not a condition from which you will recover.

“It is important that, having been tempted to commit a serious offence such as this, you are under some form of supervision for the rest of your life.”

The head of the Wales Extremism and Counter Terrorism Unit (WECTU) said he hoped the life sentence would serve as a deterrent to others at risk of radicalisation online.

Detective Superintendent Jim Hall also said police and partner agencies would continue to work together to share information on the teenager to ensure there is a robust and effective risk management plan in place for the entirety of his sentence.

Mr Hall said: “This case has highlighted the ongoing concerns with young people gaining access to extremist material on the internet and how quickly that can lead to radicalisation.

“This individual actively sought out that material, and as he became radicalised his behaviour quickly became a concern.”

The senior officer added: “We urge people to speak to a family member, teacher or us so that we can intervene at the earliest opportunity to keep the public safe.

“You will not get into trouble by reporting concerns.”

Urging the public to remain vigilant but stressing that South Wales was one of the safest areas to visit and enjoy, Det Supt Hall added: “WECTU will continue to protect local communities by working with MI5, other partners and the CPS to pursue and prosecute all those who show support for illegal and extremist organisations or who seek to spread hate and terror.”