The leader of the English Defence League (EDL) has quit the organisation in a dramatic move which saw him warn of the dangers of "far right extremism".

In a surprise development, anti-extremist organisation Quilliam said it had facilitated the move by Robinson and Kevin Carroll, joint leaders of the anti-Islamic group.

"I have been considering this move for a long time because I recognise that, though street demonstrations have brought us to this point, they are no longer productive," Robinson said.

"I acknowledge the dangers of far-right extremism and the ongoing need to counter Islamist ideology not with violence but with better, democratic ideas."

Robinson's personal assistant confirmed he had left the group along with 12 other senior members, raising the prospect of the organisation falling apart entirely.

Quilliam said it would help Robinson in his criticism of extremist Islam while assisting him in fighting off the rise of far-right activism.

It called on his followers in the EDL to follow in his footsteps and offered a similar message to Islamist extremist leaders.

"As well as being a very positive change for the United Kingdom, this is a very proud moment for Quilliam," Quilliam chairman and co-founder Maajid Nawaz said.

"This represents not a change but a continuation for us, as challenging extremism of all kinds forms the basis of our work.

"We have been able to show that Britain stands together against extremism regardless of political views and hope to continue supporting Tommy and Kevin in their journey to counter Islamism and neo-Nazi extremism."

Robinson and Carroll will hold a joint press conference at an undisclosed location in London later today to field questions.

The EDL gradually took over as the main group on the far-right of UK politics from the BNP over the last five years, after the latter group was torn apart by internal divisions.

Composed mainly of former football supporters, it has adopted an extremely aggressive approach to street protests in predominantly Muslim areas, not least by demonstrating in Woolwich following a terror attack there earlier this year.

The most difficult day of my life! I thank Edl supporters for their messages of support . For me this is a step forwards not backwards — Tommy Robinson EDL (@EDLTrobinson) October 8, 2013

I'm overwhelmed by the messages of support from Edl followers . I'm surprised but extremely grateful . I gave my life to the Edl. #newera — Tommy Robinson EDL (@EDLTrobinson) October 8, 2013

Robinson has always been a mercurial personality at the top of the organisation.

He has gone under several names and has a string of criminal convictions.

The Quilliam move suggests the organisation believes it can neutralise the threat from the far-right by bringing its leaders into the mainstream and getting them to give up on street tactics.

That mission will itself be controversial, with some anti-racism campaigners likely to prefer a no-platform alternative, which would isolate potential far-right organisations.