Undercover officers infiltrated the Luton chapter of the banned group Al-Muhajiroun and secretly recorded speeches over 20 months, including some at a local church.
Police have not revealed the name of the church where the jihadist meetings took place for security reasons.
Five men who gave speeches or helped arrange the meetings were jailed at the Old Bailey for between two-and-a-half years and six years.
Group leader Mohammed Istiak Alamgir, 37 (above, left), who hailed the Tunisia terror attack as a "victory", was sentenced to six years in prison.
Judge Michael Topolski QC told Alamgir: "You are in my judgment deeply committed to an extreme and violent jihad.
"You are a dangerous man."
The other sentences:
Yousaf Bashir (main picture, right): four years and six months
Rajib Khan: five years
Zaiur Rahman: two years and six months
Mohammed Choudry: four years
Judge Topolski concluded: "It is clear from their verdicts that the jury were sure these defendants knowingly crossed the line between a legitimate and lawful expression of deeply help opinions and beliefs and the crime of encouraging support for a bloodthirsty terrorist organisation which will not stop short of barbarity in its desire to impose upon the unwilling its corrupt version of a great and noble religion."
