A radical preacher in Britain faces a decade in prison for encouraging support for the Islamic State group.

Anjem Choudary, a 49-year-old firebrand who has been one of the best-known faces of radical Islam in Britain for years, was convicted in July and is due to be sentenced on Tuesday. Authorities see him as a key voice radicalizing young Muslims.

He gained attention for headline-grabbing statements that provoked outrage but stayed within the bounds of the law, such as protesting outside the U.S. Embassy on the anniversary of Sept. 11.

But the London-born preacher ran into trouble in 2014 after his name appeared on an oath declaring the legitimacy of the "proclaimed Islamic Caliphate State."

Choudary said the oath had been made without his knowledge.