Although the group explicitly condemns violence, Mr. Nawaz said buried in the literature is an ideology that inevitably leads to violence. He wrote on his blog that he was “duty-bound to redress the phenomenon of politically inspired theological interpretations.”

He said he helped found Hizb ut-Tahrir in Pakistan when the group sent him there in 1999, soon after Pakistan declared itself a nuclear state. The leadership believed, he said, that a nuclear Pakistan was essential for the coming caliphate. Over nine months, he formed a cell of 10 members in the area around Lahore. He was so successful, he recalled, that he steered a regional commander of the terrorist outfit Lashkar-e-Taiba, a militant group that fights India over Kashmir, into his group. The Pakistani government banned Hizb ut-Tahrir in Pakistan after the Sept. 11, 2001, attacks.

Image Maajid Nawaz was sentenced in Egypt for spreading the beliefs of Hizb ut-Tahrir. Credit... Brijesh Patel for The New York Times

In Denmark, where Mr. Nawaz traveled on weekends from Britain after his return from Pakistan, he said he recruited five Pakistani Danes into the group’s first cell there. In Britain, Mr. Nawaz was a familiar figure on the Islamic circuit, persuading university students in London to join up when he was at Newham College and later at the School of Oriental and African Studies.

One of the basic texts by the group’s founder, Taqiuddin al-Nabhani, a Palestinian judge, said it was obligatory for Muslims to militarily overthrow “every single Muslim government, then forcibly unite them into one military state even if it means killing millions of people,” Mr. Nawaz said.

Such beliefs written in the early 1950s were, he said, an ideological corruption of Islam as a religion. But Mr. Nawaz does not think the group should be banned, though he would like to help diminish its influence. He says that he believes in a tolerant society and that he is too much of a liberal to call for the abolition of the group in Britain.

Mr. Nawaz is the product of a third-generation British Pakistani family. His father recently retired as an oil engineer, and his mother works in a bank; they live in Essex, a middle-class area south of London.