At least eight suspects worshipped at the Masjid-E-Umer mosque regularly, three of whom were well known to those that run it.

Waheed Zaman, 22, lived opposite the mosque on Queens Road, and is believed to have prayed five time a day. Zaman, a final-year biochemistry student at London Metropolitan University, is understood to have become friends there with Ibrahim Savant, 25, a white convert to Islam, and Muhammed Usman Saddeque, 24. All three were known as “good Muslims” to mosque officials.

Savant is believed to have converted to Islam about five years ago.

It is understood that the Hussain brothers, Umair, 25, Nabeel, 22, and Mehran, were all frequent worshippers at the mosque, though they are known to have worshipped at others in the area. They used to sell alcohol-free perfumes outside mosques during prayer times.

All three brothers are believed to be students at universities around London.

A senior Muslim leader said brothers Assan Abdullah Khan, 23, and Waheed Khan, 25, also visited the mosque.

The Umer mosque, which is one of the biggest in the area with a capacity of about 1,300, adheres to the strict Deobandi sect of Sunni Islam, which derives from the Indian subcontinent.

No extremist Muslim groups have infiltrated the mosque but it is believed that local fanatics have distributed leaflets outside during prayer times.

Iqbal Mehtar, a trustee of the mosque, said: “Every mosque has that problem. There is nothing we can do about it.”

The mosque does allow a missionary Islamic group, Tablighi Jamaat, to preach inside. The sect is known for its tendency towards secrecy.

Western security services have in the past accused the global Tablighi movement of being a “conveyor belt” for terrorism.

However, members of the Tablighi Jamaat say they do not advocate any kind of terrorism or violence, and forbid their followers from discussing politics during prayers.

The Umer mosque, which was formerly a synagogue, was reopened after a refurbishment that cost more than £2m three years ago.

This weekend friends of Zaman rallied in support of the arrested men outside the mosque. Mohammed, 24, a fellow student at London Metropolitan University, said: “Wahid used to do a lot of community work on his own. He used to go and force people to get off drugs. He used to preach to them about Islam.”

Another friend of Zaman, who identified himself as Ali, 30, said: “Look, this mosque has had no problems with extremism. It’s just a normal mosque.”

The IT consultant added: “These people they have grabbed cannot be the people they really wanted because if British or US intelligence are saying they are capable of bringing planes down then we are very worried. These are very simple people who would not be able to do this.”

Last week, after Friday prayers, Maulana Shoaib, the imam of the mosque, appealed for calm.

Reading from a statement, he said: “The Masjid urges the Muslim community to remain calm and assist the authorities with the ongoing investigation.

“We urge all to be mindful of the fact that despite what is said in the media people are innocent until proven guilty.”

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