BBC: Right-wing groups like the English Defence League are turning parts of Britain into recruiting grounds for Islamic extremists, police have said.
The EDL emerged last year and has held demonstrations in a number of towns and cities against radicalisation.
But the West Midlands Counter Terrorism Unit has told BBC Radio 5 live there is evidence EDL events can encourage extremists.
Officers also say they are worried about radicalisation inside prisons.
Many EDL demonstrations and counter-demonstrations have ended in violence, and Det Supt John Larkin says they have witnessed signs of radicalisation afterwards.
"In some areas, we have evidence that once they have gone and the high-profile policing of the event has occurred, there's fertile ground for those groups who would come in to encourage people to have this reality - this is the way white Western society sees us," he said.
"And that's a potential recruiting carrot for people and that's what some of these radicalisers look for - they look for the vulnerability, for the hook to pull people through and when the EDL have been and done what they've done, they perversely leave that behind."
EDL leader Tommy Robinson said it was "ridiculous" to blame his organisation.
"9/11 was our fault, 7/7 was our fault, there's been 17,000 terrorist attacks since September 11th, I guess they're our fault," he said.
"I guess the last 1,400 years of history, where Islam's been at war with non-Islam, is our fault. It's ridiculous.
"We're not the cause. The root cause of the problem is the Koran, it's Islam." >>> Phil Mackie, Reporter, BBC Radio 5 live | Friday, November 19, 2010
