From the tactical froth of a dispiriting election campaign, a monstrous beast raises its head once more. Long after the twists and turns of this particular political contest are forgotten, we shall still be dealing with the poisonous ideology that spawned the horrors of Manchester and, now, of London Bridge and Borough Market. Whichever party wins on Thursday, the threat of Islamist extremism will remain a generational challenge.

Theresa May's response to London Bridge attack is tougher than after Manchester Read more

In her speech in Downing Street today, Theresa May performed the bleak tasks required of a national leader after a terrorist atrocity. She expressed shock, paid justified tribute to the emergency services, and declared the nation’s spirit would not be broken. But this time, she went further. “Things need to change,” she insisted. “Enough is enough.”

One was instantly reminded of Tony Blair’s declaration, after the 7/7 attacks, that “the rules of the game are changing”. Gordon Brown promised a battle for “hearts and minds”, accompanied by a (failed) attempt to enable terror suspects to be detained for up to 42 days without charge. In a speech in Munich in 2011, David Cameron insisted: “We need a lot less of the passive tolerance of recent years and a much more active, muscular liberalism.”

I do not believe Jeremy Corbyn would be a competent guardian of the nation’s security. He appears to believe that a readiness in the west to negotiate is all that is needed: in practice, and regrettably, terrorists negotiate only when they are exhausted by conflict and calculate that they have no more to gain from violent methods. I see no sign whatsoever of such exhaustion among Islamist extremists, in any of their battles around the world.

Furthermore, the Labour leader’s linkage of western foreign policy to terrorist acts is psychologically convenient but unsupported by the stated priorities of the jihadis themselves. In July 2016 Islamic State was unequivocal: “The fact is, even if you were to stop bombing us, imprisoning us, torturing us, vilifying us, and usurping our lands, we would continue to hate you because our primary reason for hating you will not cease to exist until you embrace Islam.”

That said, the Conservatives have an uneven record when it comes to anti-terror measures – which, during their libertarian phase, they frequently obstructed. In March 2005, for instance, the Tory whips brayed that they were off to uncork the champagne, having forced the Labour government to insert an automatic expiry date into its prevention of terrorism bill. What a revolting spectacle.

The question, as ever, is what May means by “enough is enough”. She was explicit that her blueprint does not entail a neocon plan for foreign intervention, nor a root-and-branch reform of the counter-terrorist agencies.

Play Video 6:26 Theresa May responds to ‘brutal terrorist attack’ in London

The most straightforward of her proposals was a commitment “to make sure the police and security services have all the powers they need” and, if necessary, “to increase the length of custodial sentences for terrorism-related offences, even apparently less serious offences”. This should be routine work for parliament – merely the latest iteration of its rolling review of counter-terror laws.

Much more demanding will be the battle in cyberspace and May’s challenge to “the big companies that provide internet-based services” to work with governments to prevent the spread of extremism. May is serious about taking on the tech giants and compelling them to face their function as accountable “publishers” rather than neutral “platforms”.

This distinction is not merely technical. In the new information ecology, the precise status of companies such as Facebook and Google is of the highest importance. The extent to which they accept responsibility for the content they carry has huge social implications. What is certain is that the situation has reached a critical mass, where failure to self-regulate will result in action by the state, in Britain and elsewhere. For the behemoths of the digital revolution, it really is decision time.

Most audacious – and, doubtless, contentious – was May’s charge that “there is, to be frank, far too much tolerance of extremism in our country”. Tackling this, she went on, would “require some difficult and often embarrassing conversations”. To decode: whatever problems there have been with the Prevent initiative and other counter-extremist strategies, do not think I am going to back down. No mention of “strong and stable leadership”, no sign of the so-called Maybot. These were by far the most pointed, passionate sentences May has uttered since she called the election.

British Muslims are richly entitled to ask why those who warned the authorities about the Manchester suicide bomber, Salman Abedi, were not heeded. It is also true that any undertaking that stigmatises an entire community is wholly counterproductive as well as monstrously unjust. But that does not alter the fact that May is right about Islamist radicalisation. It is marginal only in the sense that it involves a relatively small number of protagonists. Its impact is – as we have seen in the past fortnight – exponentially greater.

It is time for all Britons to unite against the common enemy by any and all legal means necessary

An ideological phenomenon that leads to the deaths of children leaving a pop concert, and the mowing down of pedestrians in our capital city, cannot be tolerated or contained with half-measures for fear of causing offence. It is not enough to identify those who become predisposed to jihadi violence: the difficult, but necessary, question to ask is what, and who, ushered them to that terrible point of departure.

Yes, this takes public policy to a delicate social frontier. But an essential feature of statesmanship is the capacity to approach that frontier with sensitivity but also without fear. The whole debate on Islamist extremism has been constricted by the crude bellicosity of some white Britons and the defensiveness of some minority groups. When nails are being pulled out of a little girl’s face and throats are being slashed in a London restaurant, such sensitivities are – at most – a second-order issue.

On this much we can surely agree: that it is time for all Britons – Muslims and non-Muslims – to unite against the common enemy by any and all legal means necessary. The unity of purpose required is much more important than the ephemeral, turbocharged division of an election campaign.

Naturally, what happens in the polling booths on Thursday is of the deepest significance. How could it be otherwise? But, compared with the global battle against this wicked ideology, the race for No 10 is, in all candour, a parochial affair.