21-year-old Al-Arfat Hassan, and a 17-year-old who cannot be named, became friends online and bonded over their extremist views.

Officers uncovered 400,000 messages after taking Hassan’s phone.

These included videos on how to commit a knife crime, and how to build an explosive device.

At the Old Bailey on Friday, Hassan was given an extended sentence of 7 years, and the 17-year-old, 3 and a half years.