Shortly after midnight Sunday, a man drove into worshippers as they departed a London mosque. Nine people were injured. One man fell ill just prior to the attack and later died.

The terrorist was motivated by his hatred of Muslims. Regardless, this attack cannot be assessed in a microcosm. There are two elements at play here.

First, there's the sustained challenge posed by ultra-nationalist organizations such as the English Defence League (EDL), British National Party and National Front. While these groups are comparatively small, they are also highly aggressive. Consider, for example, this incident in which a group of EDL supporters attacked a restaurant full of Muslim families.

That's just the tip of the iceberg. British community tensions are more significant than in the U.S.

Still, that's only the first part of the problem.

Because now, in the aftermath of recent attacks inspired or directed by the Islamic State, the British government fears that ultra-nationalist groups will be able to recruit more Britons into their ranks. In turn, the government fears that this recruitment fosters violent splinter cells and inspire lone wolf attackers. While leaders of groups like the EDL often dissuade followers from violence, increased membership does bring violently predisposed individuals together. That makes the formation of terrorist cells more likely.

Moreover, in the aftermath of emotive jihadist attacks (such as the Manchester attack on young people at a concert), ultra-nationalists are finding new impulses towards violence. Either through propaganda or tattoos, Christian-crusader imagery plays a dominant role in the life of these individuals. It illustrates the degree to which they see themselves as patriots against diversity. Speak to one of these individuals and they will tell you that Britain is in a fight for its life, and that Islam is the nation's mortal enemy.

Further complicating matters is jihadist targeting of ultra-nationalists. In 2012, for example, a major jihadist atrocity against an EDL march was only prevented when the attackers turned up after the event had ended. Police found a nail bomb, pipe bombs, swords, and firearms in the attackers' car. Had they succeeded, the EDL would have been dramatically boosted by anger amongst its target demographic: young, poorly-educated white men. Remember, the pursuit of a sectarian civil war "final showdown" is central to both jihadists and violent ultra-nationalists.All of this speaks to the British government's ultimate fear. It's worry that each successful terrorist attack encourages a sectarian response. And that, as attack begets attack, extremists on all sides escalate their chaos.