A social media website used by a British Isil supporter to urge his followers to target Prince George and send 300,000 hate-filled messages is a "mouthpiece" for terrorism, the Home Secretary has warned.

Husnain Rashid, 32, was warned that he could face life behind bars after dramatically changing his plea on a string of terror offences midway through his trial at Woolwich Crown Court.

He used the Telegram instant messaging app, which has military-grade encryption, to provide an “e tool-kit for terrorism” and called on supporters to target the four-year-old heir to the throne when he started school.

Rashid also urged followers to carry out terror attacks at next month's World Cup in Russia and encouraged them to inject cyanide into fruit and vegetables at grocery stores and poison into ice cream.

His “prolific” activities specialised in assisting the “lone wolf” attacker, urging them to carry out attacks with poison, chemicals, bombs and knives.