Two of Britain's most notorious Muslim extremists have been given free rein to recruit fellow inmates in prison and are spreading propaganda from behind bars, a think-tank founded by two former Islamic radicals said Monday. London-based Quilliam Foundation said in a report that Muslim cleric Abu Qatada - once described as Osama bin Laden's ambassador in Europe - managed to smuggle out extremist propaganda from prison with the help of visitors, who then spread his message on the Internet. It said that another radical preacher, Abu Hamza al-Masri - the one-eyed, hook-handed cleric whose extradition is being sought by the United States - was able to hold sermons through the pipes that link cells. It said another inmate used his allotted phone calls to speak to an Islamic TV station. Britain holds convicted terrorists in several high-security prisons, including the notorious Belmarsh prison in London. A Ministry of Justice spokeswoman said the conditions under which they are held depend on individual cases. In a statement reacting to the report, the ministry said British prisons are "extremely skilled in managing all challenging and dangerous criminals." James Brandon, the report's author, said the government needs to create a specialized de-radicalization center which can "de-program" extremists - a practice that has seen some success in Egypt and Yemen. "We need to take leading extremists out of the mainstream prison population and to make sure they don't radicalize other people," he said. Quilliam bills itself as a think tank dedicated to stamping out extremism. It was founded by Maajid Nawaz and Ed Husain, two activists in the Islamist party Hizb ut-Tahrir who left the group and renounced radical Islam. The report said most prison staff lack the training to recognize or tackle Islamist extremists - sometimes treating them as representatives of all Muslim prisoners and even allowing them to lead Friday prayers. The report is based largely on the testimony of prisoners, smuggled out by their supporters. It said there are now around 100 Muslims held in British prisons on charges relating to Islamist terrorism, but provided no statistics on how many people have converted to Islam while in prison. The Ministry of Justice said such information is not collected. Maha Azzam, a specialist in political Islam at Chatham House, said the report's claims may be exaggerated and could spark further distrust of the U.K.'s Muslim community. "What's clearly happening is that there is anger within prisons and Muslims feel they are picked on - this is also happening outside prisons. But will they go on to be terrorists? I don't really think so," Azzam said. "The number of those who later go on to become terrorists is very difficult to quantify," she said. The Ministry of Justice said Quilliam did not apply to visit any prisons or speak to prison staff. "We run a dedicated, expert unit which leads work to tackle the risk of extremism and radicalization in prison," the statement said. "Staff are supported with the information and training they need to deal with these individuals."