A teenage Isis supporter has admitted plotting a terror attack potentially targeting an Elton John concert on the anniversary of the 9/11 attacks.

Haroon Syed, from Hounslow, pleaded guilty to the preparation of terrorist acts between April and September at the Old Bailey after a last-ditch attempt to get his case thrown out failed.

The court heard how Syed attempted to buy weapons online, including a machine gun, handguns, a suicide vest and a bomb, and trawled the web to find crowded targets in London for the massacre.

British intelligence agents posing as fellow extremists discussed sourcing weapons, with the 19-year-old, who asked for “gear” for his “opp” in online chats.

Judge Michael Topolski QC warned Syed that he faced a life sentence on Thursday, when he adjourned sentencing until 8 June for a probation and psychiatric report to be carried out.

Syed, whose older brother was jailed separately for plotting an Isis-inspired attack on Remembrance Day, was caught after making contact with a spy going under the name “Abu Yusuf” on his phone and social media.

When asked for details of his attack, he said he needed a machine gun and an explosive vest “so after some damage with machine gun do martyrdom...that’s what I’m planning to do”.

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The pattern has been seen in numerous Isis-linked attacks, including in Paris in November 2015, when militants massacred members of the public with machine guns before detonating their suicide vests.

When Abu Yusuf said it would be costly, the defendant told him he was “broke“ but pressed on, saying: “You have to find out the price for the machine gun, any gun.”

Syed backed out of the pair’s first planned meeting, because he knew he was being followed by police, but they later met at a Costa Coffee in Slough.

Discussions over making or getting hold of a bomb and acquiring a gun continued throughout August, although Syed admitted he had never used a firearm before.

On 30 August, he told the informant that he needed a “portable” device, adding: “I might put the bomb in the train and then I’m going to jump out so the bomb explodes on the train…so ask the brother if he can make that type of bomb with button.”

He made arrangements to pay £150 for the device the following week, asking Abu Yusuf to ensure it was packed with nails and adding: “I was thinking of Oxford Street...if I go to prison, I go to prison. If I die, I die, you understand.”

The teenager had searched the internet for Isis, previous terror attacks and potential targets including an Elton John concert in Hyde Park that was held on 11 September.

Police arrested Syed three days before at his home in Hounslow, West London.

Terrorism in 2016: Terror attacks in Europe claimed by Isis Show all 9 1 /9 Terrorism in 2016: Terror attacks in Europe claimed by Isis Terrorism in 2016: Terror attacks in Europe claimed by Isis Policemen outside Rouen's cathedral during the funeral of Jacques Hamel, the priest who was killed in a church in Saint-Etienne-du-Rouvray in Normandy on 26 July during a hostage-taking claimed by Islamic State group Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two jihadists, both 19, slit Hamel's throat while he was celebrating mass in an attack that shocked France as well as the Catholic Church Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Muslims place flowers and hold a minute of silence in front of the church if Saint-Etienne-du-Rouvray, western France, where French priest Jacques Hamel was killed on 26 July Charly Triballeau/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two people hold each other by the new makeshift memorial in Nice, in tribute to the victims of the deadly Bastille Day attack at the Promenade des Anglais Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis The Islamic State group claimed responsibility for the truck attack that killed 84 people in Nice on France's national holiday. Mohamed Lahouaiej-Bouhlel, 31, smashed a 19-tonne truck into a packed crowd of people in the Riviera city celebrating Bastille Day Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police work at a site where a Syrian migrant set off an explosive device in Ansbach, southern Germany, on 25 July, killing himself and wounding a dozen others Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis A Syrian migrant set off an explosion at a bar in southern Germany that killed himself and wounded a dozen others in the third attack to hit Bavaria in a week. The 27-year-old, who had spent a stint in a psychiatric facility, had intended to target a music festival in the city of Ansbach but was turned away because he did not have a ticket Friebe/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police officers walk along train tracks in Wuerzburg southern Germany on 19 July, a day after a man attacked train passengers with an axe. German authorities said they had found a hand-painted IS flag among the belongings of the man, an asylum seeker from Afghanistan, who seriously injured four members of a family of tourists from Hong Kong in his rampage Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis German police killed a teenage assailant after he attacked passengers on a train in Wuerzburg, southerg Germany with an axe and a knife on 18 July, seriously wounding three people Karl-Josef Hildenbrand/AFP/Getty Images

When they asked for a password to lock his phone, the court heard he replied: “Yeah I.S.I.S – you like that?”

Commander Dean Haydon, from the Counter Terrorism Command, said information from members of the public triggered an investigation by Scotland Yard and MI5.

“It was information we received in respect of Syed’s change of behaviour that meant we looked at him and our close working relationship with MI5 ensured that we uncovered his plot to kill and mutilate innocent members of the public,” he added.

In legal papers prepared for his defence, Syed was described as “highly vulnerable due to family history, lack of education, addiction to violent online games and the arrest and imprisonment of his brother”.

A defence statement claimed that although he was groomed by extremists online, he never planned to go ahead with the attack and the recorded conversations were a “fantasy to see how far it would go”.

Isis recruiters are known to target vulnerable young men with online material, and have specialised in radicalising those linked to violent crime or gangs.

The communications have been linked to a series of “lone wolf” attacks committed around the world, with analysts warning that Isis is “remote controlling” massacres from its strongholds.

Syed’s lawyers attempted to get the case dismissed or exclude key evidence from online chats, but the motion failed and he entered the guilty plea.

His representative, Mark Summers QC, argued that the Government should have intervened earlier and offered the teenager help through the Prevent deradicalisation programme.

“The proper response of the state should have been to engage Prevent to help this young man, to steer him away from the path it was feared he was going down, rather than guiding him down it,” he told the court.

Syed’s brother, 23-year-old Nadir Syed, was jailed for life in June after he was found guilty of plotting to carry out a Lee Rigby-style beheading around Remembrance Sunday in 2014.