Al-Arfat Hassan, 20, appeared at the Old Bailey on Friday (November 10) and confessed that he possessed chemicals for terrorism purposes.
A Met Police spokesperson said Hassan was previously convicted in December 2022 of collecting information likely to be used for the cause too.
A 17-year-old from Leeds, who cannot be named, similarly accepted that he had gathered details that could have been useful for an ISIS propaganda video.
The young boy, who was aged 15 at the time of arrest, also agreed that he had information about terrorism acts.
Hassan reportedly became friends with the teenager online and they bonded over their extremist views.
A probe was launched into Hassan after he was stopped at Heathrow Airport on February 27 last year and officers found evidence of his extremist mind set after seizing and analysing his phone.
The investigation uncovered that Hassan bought chemicals that were ingredients for an explosive device. Videos of him posing with a sword and the chemicals were also discovered.
Several of these messages said to have contained videos and images of the teenage boy in Leeds, who was seen posing with knives and featuring flags from ISIS and other terrorist groups. He was arrested nine days after Hassan on March 12, 2022.
They were each later charged with preparation of terrorism acts. After two trials, at Leeds and Sheffield Crown Courts respectively, both Hassan and the 17-year-old boy offered guilty pleas which were accepted by prosecutors.
The duo will be sentenced on February 02 next year at a court to be confirmed.
Commander Dominic Murphy, who leads Met’s Counter Terrorism Command, called the fact that these two defendants are so young as “disturbing and saddening”.
He revealed that a growing number of young people in the country, some still in school, are being arrested for involvement in terrorist activity.
The youth, he claimed, are often radicalised by material and extremists they come across online, as was seen in this case.
He said: “We work around the clock with all our partners to tackle terrorism, but we can’t do it alone and we would urge the public to act early if they see or hear that might be linked to terrorism and contact the police. Your call could save lives.”