We are officially on notice. According to MI5, an Islamist attack in the UK in the coming days and weeks is “very likely”. Well, I could have told you that, and all I know is what I see on television.

Security is the buzz-word of our age – though, as you might expect, this is only because there doesn’t seem to be any. As Michael Gove would agree, there are more “experts” employed “keeping us safe” today than at any time in our history, World War II included. But what use are they? How much absence of bang are we getting for our bucks?

The fact that so far this year no one has been killed by terrorists in Britain should not blind us to the fact that even now, as I write, an unknown number of fanatics are working on how to carry out an attack. Many will fail. But some will succeed. If you don’t believe me, ask MI5. Or, as they do, use your common sense.

So what do we do? More to the point, what should they do?

Theresa May, until her recent elevation the longest-serving Home Secretary since Labour’s James Chuter-Ede, is hugely experienced in this area. She has sat through meetings of Cobra (the Cabinet Office Briefing Room, equivalent to America’s Situation Room) on numberless occasions, listening to the heads of “Five,” “Six,” Special Branch and GCHQ warn, advise and plead for increased resources. She knows better than anyone how vulnerable our country is to attack and how difficult it is to keep us safe.

Allowing for scale, the terrorists are a bit like the pan-Arab armies of the 1960s and ’70s, which only had to defeat Israel once to wipe out the Jewish State while the Israelis had to win every time. A successful grade 1 attack by Isil or its affiliates on a UK target – Manchester city centre, say, or York Minister, or the Trooping of the Colour – would cause convulsions across the country and raise the terrorist alert to levels not seen since the 7/7 attacks in London.

For those charged with preserving the peace, it is – barring a plausible nuclear threat – their worst nightmare. And the same is true across Europe. Even if it is a fact that scores of terrorist attacks in France, Germany, Belgium and the UK have been averted by intelligence agencies acting in concert with each other and with police across the continent, the fact remains that innocent people are dying, or being horribly maimed, on an almost daily basis. Soon, according to MI5, it will be our turn.

So I ask again, what is to be done? States of emergency are, by their nature, temporary. No nation, or its agencies, can remain at the highest state of alert for more than a few days or weeks at a time. In France, they have just discovered the truth of this in the most dramatic way possible. No sooner had they wound down from the attacks in Paris in November than they had to scale back up again after the slaughter in Nice. French people can see through this. They know that absolute vigilance cannot possibly be maintained. But they also know who is to blame when things go horribly wrong – in this case the hapless President François Hollande, his prime minister Manuel Valls and the interior minister Bernard Cazeneuve. “Out! Out! Out!” they cry.

And no wonder. It was on July 6, just eight days before the Nice attack, in which 84 people died and 303 were injured, that Valls announced that there had never been a better time to come to France. On July 12, as the Isil-inspired culprit was finalising his plan, Cazeneuve issued a statement in which he lavished praise not only on the 90,000 security personnel, including 10,000 combat troops, who had overseen the Euro 2016 football championship, but on the country’s security network as a whole who, “with the terror threat looming large,” had worked “without let-up” round the clock to keep France safe.

Noting that 150 individuals had been arrested in relation to terrorist activities this year on the basis of national intelligence, Cazeneuve laid stress on the decisive role played by the police and security services across Europe. He did not know – obviously – that a madman was about to drive a truck through a crowd celebrating Bastille Day in Nice. Nor had he any idea that two quite separate fanatics were sharpening their knives in preparation for their murder of an 85-year-old catholic priest in front of his altar in a quiet suburb of Rouen. But that is the point. The Nice assailant was known to the police. He had mental issues, a violent disposition and, as it turned out, a readiness to join the Isil death cult. Adel Kermiche, one of the two young Muslim men who this week murdered Father Jacques Hamel, was not only known to the authorities as a would-be Isil fighter, but was actually wearing a security bracelet as he slit the priest’s throat.

So I ask a third time, what is to be done?

Let us start with where we are. The British people are leaving the European Union, but we are not leaving Europe. This is what Theresa May and Boris Johnson have been telling our eventually-to-be erstwhile colleagues in Brussels, Paris and Berlin. In matters of defence and security, we will be with you. In the fight against terrorism, we will be as one.

The trouble with this is that Europe already has more safeguards in place against terrorism and mass migration from Muslim countries than you could throw a stick at. We ought to be in fine fettle – except that we’re not. Europe has ended up like Winterfell out of Game of Thrones – a stronghold and symbol of power and authority that is under permanent siege, with death and destruction at every turn.

I hesitate to write this … but might it not be time to establish an all-new European Security Agency, based, I would suggest, in London, that concentrates exclusively (or until some equivalent threat takes its place) on the threat posed by Islamist terrorism? Such a body would not concern itself with Russia, or North Korea, or China’s expansion into the western Pacific. It’s sole purpose would be to identity and nullify those who are plotting to kill us in our own streets and places of worship.

But, you might argue, do we not already have Europol, based in the Hague, with its 940 employees and annual budget of £85 million? And is it not already the case that the intelligence agencies of France, Germany, Italy and elsewhere (to say nothing of the US-led “Five Eyes” network) are already working together, overseen by a raft of interior ministers and their advisors?

Well, 940 is significantly less than half the number of officers in the Durham Constabulary, one of the smallest in the UK, with its current budget of £113 million. If what the Leave side told us during the referendum campaign was even half-true, the amount spent on Europol every year is roughly equivalent to what Britain pays into the EU each week from Monday to Wednesday. Moreover, Europol was really intended to tackle fraud and organised crime and those individuals who cross Europe’s borders to escape justice at home. It has no executive authority, no powers of arrest and only limited authority to conduct investigations on the ground.

As for existing inter-agency cooperation, it is entirely voluntary. Its successes are real. But the structure is weak, based on personal ties, “trust” and so-called “need to know”. And while Five Eyes might warn of us a coming nuclear attack or Russian invasion, it does little to inform us of the murderous intentions of a group of zealots plotting a suicide attack from a council house in Rotherham. What is actually required is a fully-funded, over-arching body that functions at all levels, not just at the top, receiving unfiltered, active intelligence day-in, day-out, from officers and informants who work the streets, housing estates and corner cafés of Europe, from the Turkish frontier, via downtown Munich to the “Jungle” of Calais.

An infringement on our sovereignty? Live with it. This is war. A diminution of our freedoms? So is being blown up or machine-gunned when we go out for a drink with friends. The new agency would have nothing to do with the EU. It would not be governed by treaty. Vitally, it would have to be regulated and watched over by national parliaments, including our own, to ensure that it did not become an anti-Muslim version of the Stasi. Beyond that, while earning the trust of all law-abiding citizens, it would have to prove its worth. It would have to defeat Isis in Europe within a reasonable time and restore a sense of safety to our continent. The alternative – by far the most likely option – is that we carry on exactly as we are, reluctantly endorsing what Tory Home Secretary Reginald Maudling, in reference to Northern Ireland, once called “an acceptable level of violence”. Is that what we really want? I think not.