Police have been criticised for not treating the tragedy – which saw the gunman shoot five people and himself, after misogynistic social media posts calling himself an involuntary celibate – as terror-related.
Jonathan Hall, the independent reviewer of terrorism legislation for the Home Office, said whether or not a threat is categorised as terrorism is a “question of scale”.
But he added: “If we see more of these sorts of attacks, then I have got no doubt that it will be treated more seriously as terrorism.”
Incels, who typically blame women for a failure to form sexual relationships, are currently considered part of right-wing terrorism – but Mr Hall acknowledged they are “quite separate”.
Davison said he was an “incel” and protested about not losing his virginity as a teenager, in a rambling video posted on YouTube three weeks ago
On a Reddit account, one post was titled “Why anti-gun people are evil & disgusting human filth”. He also described women as “very simple-minded and they ain’t all that bright”.
Mr Hall, said there was no need to change the definition of terrorism, because the current description of violence used to advance an ideological cause is sufficient.
He told BBC Radio 4 that an “isolated incident” crossing that threshold would probably not be treated as such because it might not make sense to “divert resources” to counter it.
But he added: “If something reaches a scale where it affects, if you like, the national security of the country or the general sense of security, of the population, then you might want to.”
Mr Hall added, on the incel threat: “It seems part of right-wing terrorism but it is not really. In fact, it is quite separate from it. It is a different sort of ideology.
“The question is really one of choice. Do we want to start treating incels as potential terrorists?”
Peter Fahy, the former chief constable of Greater Manchester Police, agreed that many people believe misogynistic crimes are “not high enough” on the list of police priorities.
But he added: “When we give high publicity to these cases, which is inevitable given the size of the tragedy, the trouble is it puts thoughts in other people’s minds. We must be careful we don’t build these people up too much.”
Nazir Afzal, formerly chief crown prosecutor for the north west, also questioned why Davison was not on a police watchlist, saying he was “exactly the type of person the authorities should be keeping an eye on”.
In his now-deleted posts, Davison set out his hopes for “making up” for missing out on a sex life as a teenager.
He was a gun enthusiast who praised Donald Trump, and wrote regularly of his hatred for his mother, Maxine, who was the first person he shot dead.
Neil Basu, Britain’s most senior counterterrorism officer, warned MPs a year ago that young people were being groomed online for terrorism, including “incel” alongside far-right and Islamist extremism.
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