From that link:

What research does show is that we may be more likely to find lone wolves among far-right extremists than among their jihadi counterparts.

("What research does show" is weasel words, but hey).

Just thought I'd mention it in case the length of the piece defeats anyone. He goes on to discuss Jo Cox's killer and some other far-right examples. If the word terrorism immediately evokes "Islam" in your mind, you need to examine your conscience.

The fact remains that we can't identify what the Westminster killer's motive was, or know whether he was mentally deranged at the time. Broad-brush analysis of the kind the article deals in is perfectly legitimate; individual cases have their own unique features.