At a religious conference in Birmingham three months ago, a bearded cleric wearing a white turban shook with anger as he wagged a finger at his audience. The over-amplified voice of Mumtaz ul Haq echoed around the room while he hectored his audience about the differences between Sunni and Shia Muslims.

This was no thoughtful theological discussion, however. Mr Haq’s lecture, available on YouTube under the title Shia Exposed, condemned the minority denomination as non-Muslims. “Such people are not just kafir [non-believers], they are kufoor [a worse category of non-believer],” he cried.

At the talk, during a conference in Birmingham in May, he went on to vilify Shia texts and scholars, personally insulting Ayatollah Khomeini, the founder of Iran’s Islamic revolution, who remains revered by many Shia Muslims. “People say Imam Khomeini, I say Shaitaan Khomeini,” he said. Shaitaan is the Arabic word for Satan.

Divisive sermons such as that of Mr Haq, a prolific preacher from south London, are becoming increasingly common in mosques, at prayer circles and on university campuses.

The preacher belongs to the Deobandi school of Sunni Islam, which according to Innes Bowen, who wrote the study Medina in Birmingham, Najaf in Brent, controls 45 per cent of mosques in Britain and almost all the training of Islamic scholars in the country.

If Mr Haq’s diatribes are causing concern, many Shia Muslims have been downright frightened by sermons delivered by Khalid Fikri, an Egyptian-born Islamist preacher who has lived in Britain since 2005 and is believed to have political asylum.

Dr Fikri delivers lectures with titles such as Shia: The Reality andShia: The Danger. Some are delivered from the sofa in his home in north London, others are recorded at mosques, prayer meetings and on university campuses across the country. The Islamic Society at Birkbeck, University of London, hosted a Ramadan talk by him in June called The Path to Paradise.

In one lecture, The Agenda of the Shia, uploaded to the internet in 2013, Dr Fikri highlighted the sectarian aspects of the Syria conflict while addressing an audience in Britain. “They [the Shia] kill us with faith,” he said. “[They believe that] killing the Sunni is to raise your rank in paradise. Raping a Sunni woman is a matter that pleases Allah. Shia are one of the worst and greatest enemies of our ummah[Muslim community] nowadays.”

The sectarian preaching is not all one-sided. Yasser al-Habib, a Kuwaiti Shia preacher, operates from a mosque in the village of Fulmer in Buckinghamshire. He is believed to have political asylum in Britain after fleeing Kuwait, where he had been jailed for an offensive verbal tirade against the wives and companions of the Prophet Muhammad. He has amassed a significant following to his sermons and his Fadak TV channel.

Mr Habib has described Wahhabism, the fundamentalist form of Sunni Islam practised in Saudi Arabia, as “a criminal and violent ideology, founded by a mentally ill man”. Mainstream Shia leaders have condemned Mr Habib and maintain that he is a marginal figure with a small following who does not represent their faith.

Sayed Ammar Nakshwani, a British preacher now based in the United States, said of Mr Habib: “We have some disgraceful representatives. On YouTube today you will find people dressed like clerics hiding in a house in London and sending curses on personalities revered by others in Islam. I may disagree with those personalities, but do not talk offensively — people in Peshawar, Bahrain, Iraq, die because of our lecturers.”

Moderate Sunnis were also quick to distance themselves from sectarian rhetoric. Qari Muhammad Asim, imam at Leeds Makkah mosque, said: “Our faith doesn’t condone takfir [excommunication] of another. This increasing takfir rhetoric is a cancer eating away at the Muslim community.”

The preachers defended their words. Mr Haq said that he never preached violence. “I see my role as a defender of my faith. It’s an issue of theology and they are in response to hatred from Shia scholars against our revered figures.”

Majid Obaidi, a spokesman for Mr Habib, said: “Sheikh Yasser is the only one in present Islamic history to say these things and he is right.”

Dr Fikri could not be contacted yesterday.

By Faisal Hanif and Sean O’Neill – The Times UK