Cheering for Osama, by the think-tank Quilliam, describes the website as the “mouthpiece of the most extreme and bloodthirsty strand of jihadism”.

It says the Arabic-language site is a “jihadist” discussion forum which “regularly praises suicide bombing, the death of British and Nato soldiers and incites hatred and violence against Iraqi Shias, Jews and Westerners”.

It is unclear why the Medad al-Suyuf site has not been shut down, but it may be because the site is not in English and had not previously been traced to Britain.

It is registered to Walid ElSharkawy, a British national of Egyptian decent, who lives in Camden, North London, according to public records.

Mr ElSharkawy, 46, describes himself as an IT technician and is married to, but separated from, Mary O’Sullivan, 52. They had a child, Salma, who was taken into care at the age of 10 and died three years ago in a car crash at the age of 12.

Last night Mr ElSharkawy was unavailable for comment.

The Medad al-Suyuf website has 4,000 registered users who are encouraged to follow a “hard-line view” that “essentially gives carte blanche to carry out acts of violence and to ignore any criticism or calls for calm, even if this comes from senior pro-Jihadist writers and preachers”, the report says.

The site is said to support the violent tactics of Abu Musab al-Zarqawi, a former leader of al-Qaeda in Iraq who produced videos in which the hostages Ken Bigley and Margaret Hassan were executed.

A regular contributor to the site is Abu Qudama Salih al-Hami, Zarqawi’s brother-in-law, who lives in Jordan.

Others include Yasser al-Sirri, an Egyptian member of Islamic Jihad who was convicted in his absence for his alleged role in an attempt to assassinate the Egyptian prime minister in 1993. He lives in London and has been arrested three times in relation to plots in Yemen, Afghanistan and the US, but never charged.

Another contributor is Muhammad al-Massari, a Saudi-born physicist who has lived in London since 1994 where he was in touch with Osama bin Laden before 9/11 and has helped run the radical groups Hizb ut-Tahrir and al-Muhajiroun. He also runs a website called al-Tajdeed.

Quilliam, a counter-extremist think tank founded by former radicals Ed Husain and Maajid Nawaz, called for those behind the site to be prosecuted under the Terrorism Act for glorifying terrorism and stirring up racial hatred.

It also says the Government should raise the separate issue of Wahhabi clerics with the government of Saudi Arabia which sponsors them.

Mohammed Ali Musawi, the author of the report, said: “Jihadists clearly regard those who subscribe to the Wahhabi view on jihad — that religious violence against non-believers is permissible but that it must be sanctioned by an authentic Islamic state — as only a few degrees away from jihadism.”

The report says that Wahhabis “should be excluded from preventive counter-radicalisation efforts”.