A banned cleric is still preaching support for terrorism to young British Muslims by appearing incognito on the internet, the BBC has learned.
The joint investigation by File on 4 and Newsnight has found Omar Bakri Mohammed broadcasts hatred for the UK using a variety of pseudonyms.
He was excluded from the UK last August on the grounds that his presence was "not conducive to the public good."
On a recent broadcast he said the 7/7 London bombers were "in paradise."
The BBC investigation has also revealed how young British Muslims are being radicalised by extremists on university campuses and in street gangs.
Omar Bakri Mohammed ran the radical al-Muhajiroun group from Tottenham, north London, until it was proscribed last year.
The then Home Secretary Charles Clarke barred him from returning to Britain while he was out of the country in August 2005.
But the BBC has learned that he broadcasts online most evenings - a voice recognition expert confirmed that the voice was that of the radical preacher.
In one broadcast he praised the 2005 London bombers by saying: "How can you condemn those great men - it's not something so bad, something so good. Something so good to be involved in."
A chatroom has been infiltrated by a group called Vigil, which aims to disrupt radical groups and report back to police and security services.
During an online question and answer session a Vigil member asked Omar Bakri Mohammed if Dublin Airport should be a terrorist target because US troops transit there on the way to Iraq.
The cleric replied: "Hit the target and hit it very hard, that issue should be understood. Your situation there is quite difficult therefore the answer lies in your question."
Vigil claims the UK authorities have been slow to deal with the broadcasts.
One academic, who is a member of Vigil, contacted the Metropolitan Police's anti-terrorist hotline saying he had more than 100 hours of material from the chatroom only to be told to contact his local police station.
"The anti-terrorist office showed no sense of urgency to get this information," he said.
Home Office Minister Tony McNulty said he would examine the details of the claim.
He also said: "Glorifying terrorism on the internet is an offence and we are trying to deal with it and keep up with it.
Mr McNulty added: "We do have to keep these things under review."
Hear the full story on Radio 4: File on Sun 12 Nov 1700GMT or online at the File on 4 website
See the full story online at the Newsnight website