Christchurch has turned everyone’s attention to the phenomenon of extreme rightwing terrorism. But it is an alarm bell that authorities in the UK have been ringing for some time, having seen an ascendant extreme-right threat. Our collective attention, when thinking about terrorism, may be dominated by Isis, but given the rich vein of references to the UK in Brenton Tarrant’s screed, there are clearly other concerns to which we should pay attention.

Around the turn of the century and during the early noughties, the extreme-right threat in the UK tended to consist of a ragbag of isolated loners. For the most part middle-aged white men, they tended to be discovered by chance – violent characters with spotty employment histories, a few of them picked up as a result of investigations into online paedophilia. Some particularly shambolic cases, such as that of Neil Lewington, were uncovered by accident. Lewington was arrested by British Transport police after urinating on a train platform in 2008. Subsequent investigations uncovered an aspirant one-man terror campaign, planning pipe-bomb attacks and gathering Nazi memorabilia.

This pattern has now changed. An early indicator was Pavlo Lapshyn’s terror campaign in the West Midlands in 2013. Arriving from Ukraine on a scholarship, he immediately launched an attack on the Muslim community, starting by killing elderly Mohammed Saleem in a murder that baffled police. He then started building bombs of escalating potency that he left outside mosques in the West Midlands.

Fortunately, while Lapshyn was an expert bomb-maker, he got his timings wrong and all three of his devices failed to kill anyone. When police caught him they discovered that he had a history of bomb-making back home in Ukraine and was deeply embedded in online extremist communities.

The case marked a worrying evolution. Here was a well-organised young man with capability and ideology. The fact that he was from another part of Europe showed the potential for extreme ideologies to spread across the continent. He also reflected broader links between extreme rightwing communities in the UK and continental allies.

The threat in the UK became even more pronounced with the emergence of National Action. Part political action group, part online community, part terrorist group, NA brought together a cluster of angry men around a xenophobic ideology focused on committing acts of terror and fighting back against a society they believed had been overrun. In contrast to earlier iterations of the extreme right in the UK, National Action’s members were mostly younger men.

There is a distinct trajectory here: from disorganised loners to semi-structured networks, and ideologies that are no longer isolated in national geographies, but speak to global communities who feel left out. A narrative is developing of an ascendant extreme right that is becoming more organised on our shores and has links abroad.

More disturbing is the degree to which we can see evidence that these ideas have originated in our country. Prominent among Tarrant’s ramblings are references to British fascist leader Oswald Mosley. We have a sad history of intolerance in our public discourse, and its mainstreaming in an increasingly febrile public forum creates a context for violent extremists to believe the time for action is now. We have already witnessed the murder of Jo Cox, and Darren Osborne’s attack on Finsbury Park mosque. It is essential to clamp down on it before it tears further at society’s fragile fabric.

Raffaello Pantucci is director of international security studies at the Royal United Services Institute

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