The far right, to win votes, capitalises on a fear of Muslim extremism, especially terrorism. That aids extremists by playing into a narrative long cultivated by a spectrum of radicals, including Osama bin Laden.
In this narrative, Islam is under attack from western Christian nations as part of a clash of civilizations. Muslim-bashing in the West becomes further evidence that Muslims are unwelcome in these places and will never be accepted because of their religious faith. Alienation rises, and the most alienated are drawn into the web of the extremist recruiters and potentially into terrorism cast as defenders of the faith. If a terrorist act ultimately occurs, then that is more fuel for the far right. And so on and so on in a potentially long-running cycle.
If this cycle has begun and when it will end are questions that go far beyond the English Defence League and indeed beyond "England".