Last week’s terrorist attack in London, which left four people dead, wounded dozens more and led to the temporary lockdown of Parliament, was a grim reminder of the daily threat Europe faces from extremist violence.

It also showed the challenges for intelligence and security services in confronting individuals who, like the 52-year-old attacker, British-born Khalid Masood, are intent on causing mayhem and destruction armed with low-tech weapons, such as sports utility vehicles and kitchen knives.

British authorities are still trying to understand how the attacker, who was not considered a serious terrorist threat by British security services, had become radicalised, whether he acted alone and if he received instructions from handlers in Britain or abroad.

This juncture raises broader questions about the nature and scope of Europe’s terrorist threat, and how best to respond to it.

Low-cost techniques

Last week’s attack shared a number of similarities with several other recent terrorist assaults across Europe. Rather than hatching a complex plot using guns or explosives, Masood mowed down pedestrians crossing Westminster Bridge and stabbed a police constable guarding the Palace of Westminster before being shot and killed by police.

A day after the attack, ISIS claimed responsibility, releasing a statement calling Masood a “soldier of the Islamic State”. But it is not yet clear what connection, if any, he had with the group.

Still, his method of attack came right out of the ISIS playbook. Since early 2014, ISIS has encouraged its supporters to use vehicles to inflict mass casualties. Last July, a truck plowed through crowds gathered to celebrate Bastille Day in Nice, France, killing 86 and injuring hundreds more. In December, a truck drove into a Christmas market in Berlin, leaving 12 people dead and dozens more wounded.

Just a day after last week’s London attack, a French resident of North African ancestry tried to drive over pedestrians on a crowded shopping street in Antwerp, Belgium. Police were able to stop the assailant before he inflicted harm. A search of the vehicle turned up a rifle and several knives.

Petty criminals and terrorist ‘diaspora’

Masood typifies one type of terrorist threat facing European countries today: native born, with a criminal past but not sufficient to be considered a major terrorist threat and no clear connection to terrorist cells or networks operating in Europe or elsewhere, who opts for low-tech means of spreading carnage and terror.

As European authorities have improved efforts to thwart complex, large-scale attacks such as those in Paris in November 2015 or in Brussels in March 2016, the type of attack witnessed in London last week may become more prevalent.

European countries must also cope with fighters returning from Syria and Iraq, many of whom are battle-hardened and brimming with jihadist ideology. Europol, the EU’s law enforcement agency, estimates that 5,000 Europeans went to fight with militant groups in Syria and Iraq. As many as 1,000 of these fighters have returned to Europe.

And, as ISIS has lost territory in Syria and Iraq, its leaders have made Western targets a higher priority. Some of these returned fighters have formed terrorist cells and networks to plan and carry out future attacks.

Weak security cooperation in Europe

The increase in terrorist attacks in Europe in recent years has lead to calls to establish closer counter-terrorism cooperation among European intelligence and domestic security services.

Because of Europe’s open internal borders, terrorist networks are free to move around the continent. Intelligence and law enforcement agencies, on the other hand, still operate largely within their own national borders, giving terrorist groups an opportunity to exploit gaps or weak links in Europe’s counter-terror defences.

The EU has always been more about economic cooperation, so national security is and will remain the primary responsibility of member states.

Intelligence sharing among EU countries remains spotty. It is a huge challenge to effectively coordinate intelligence and police cooperation across 28 countries. Even after decades of integration, a number of practical, legal and political hurdles impede EU information-sharing and counter-terrorism efforts.

European countries judge terrorist threats differently, have divergent laws governing domestic intelligence and law enforcement activities, and face wide variation in the degree of professionalisation of national intelligence and domestic security services. A lack of trust prevents the sharing of sensitive information, particularly with those Eastern Europe countries that were under communist control just a generation ago.

The EU has taken various steps to facilitate better cooperation among member states. It has had a counter-terrorism coordinator since 2004, implemented a continent-wide arrest warrant that expedites the extradition of terrorism suspects, established a counter-terrorism centre within Europol, and approved passenger name records (PNR) for flights entering and departing the EU.

But Europol’s budget and manpower remains limited, and these measures can only go so far. Europol does not have operational powers (like the FBI does, for example), and it lacks the authority to make arrests. The European Counter Terrorism Centre provides some strategic analysis but relies heavily on information from member states. And no EU country has fully implemented the PNR directive yet.

No easy or quick solutions

The scale and complexity of the terrorist threat are straining European intelligence and security services. Governments are spending billions on enhanced domestic security measures and on tracking and monitoring thousands of suspects.

France has as many as 15,000 suspects on its terrorism watch list. At any given time there are over 500 ongoing counter-terrorist investigations in Britain.

Even at a time of heightened security, last week’s attack — the worst terrorist attack on British soil since the July 7 2005 London transport attacks, which left 52 dead and hundreds injured — showed the ability of a committed individual to inflict casualties in the heart of a major European city.

There have been successes. British authorities announced that 13 terrorist attacks have been thwarted in Britain since 2013, and French authorities have foiled a number of plots in recent years, as have other European nations.

The terrorist threat facing Europe today is a permanent one that defies easy or quick solutions. Its long-term impact will depend on how societies respond to this challenge. As former British prime minister Margaret Thatcher said after a terrorist bombing in 1984, “Life must go on, as usual.”

Richard Maher, Research Fellow, Global Governance Programme, Robert Schuman Centre for Advanced Studies, European University Institute

This article was originally published on The Conversation. Read the original article.