Extremist preacher Anjem Choudary is wrongly seen as "a figure of fun" while his banned Islamist movement Al-Muhajiroun acts as "a conveyor belt to terrorist groups", campaigners have claimed.
Hope not Hate has published a report alleging that the controversial figure has given justification to terrorist plotters with his outspoken views and that the banned group is "the single biggest gateway to terrorism in recent British history".
Mr Choudary said that al-Muhajiroun has been active since the 1990s meaning that a lot of people will have come into contact with the group, but denied any involvement in atrocities.
The Hope Not Hate report said: "While painted by some in the media as a figure of fun, an extremist crackpot whose often outlandish media stunts are rightly ridiculed, Anjem Choudary has become a serious player on the international Islamist scene. Perhaps it is time to stop laughing at his ridiculous stunts."
It goes on: "While there is no evidence to prove that the group's founder Omar Bakri Mohammad, or its current leader Anjem Choudary, have directly instigated any terror plots we do believe that they have given people the justification and encouragement to take extreme actions. Some have organised terror plots whilst still active in the al-Muhajiroun while for others it has been a conveyor belt to terrorist groups.
"Al-Muhajiroun has quite simply been the single biggest gateway to terrorism in recent British history."
The group was banned in the UK in 2010, and a study suggested that in the preceding 12 years 18% of Islamic extremists convicted of terror offences in the UK had current or former links with the group.
Mr Choudary said: "Hope not Hate is trying to say that we are behind every terrorist operation since 7/7. If that was the case surely the police would have come and arrested us?
"There are a lot of fanciful ideas.
"A lot of people have come across us. The July 7 and the July 21 bombers probably came across us at one point but that doesn't mean that they were members of our organisation. If they were the police would have come to talk to us about it."
"We've been saying the same thing since the 1980s and no one was going out and carrying out military operations. The only thing that has changed is the British government's policies."
Earlier this year Scotland Yard said that they were "constantly assessing" whether Mr Choudary's proclamations were breaking the law.
The Hope not Hate report also claims that a video recently released by terrorist group al-Shabaab, who were behind the massacre in the Westgate mall in Kenya, was narrated by 21-year-old Londoner Mohammed Hasnath, who it claims also had links to al-Muhajiroun.
He was jailed for 14 months last year for possessing terrorist documents, after previous brushes with the law for spray-painting burkas on adverts featuring scantily-clad women and putting up "gay-free zone" posters in east London.