One of the inevitable consequences of the Paris terrorist attacks is that France will need to spend more on security, especially on intelligence. So will most member states of the Schengen area.

Schengen is the name for the passport-free travel zone made up of 26 European countries, including 22 EU states. Last week it became clear the security network that supposedly operates quietly and efficiently in the background of Schengen is not working. The death of Abdelhamid Abaaoud during a police raid on the Paris suburb of Saint-Denis was at one level a big success. The police got the suspected terrorist who co-ordinated this and other attacks. On another level his death was also a nasty shock. What does it say about Schengen if one of the world's most wanted criminals was able to move freely between Syria, France and Belgium? That was not supposed to be possible.

There are, in principle, two fixes. Repair Schengen; or revert to national systems. Both work. The first would be economically efficient but is politically hard to do. The second is politically easier to do, but would constitute a spending shock of macroeconomic scale for many countries.

Regain trust

The repair of Schengen would have to go beyond the unambitious agenda of justice and interior ministers, who met last Friday to consider a few practical proposals. The problem with Schengen is that within a few weeks it has lost its biggest asset – the trust of the population. French president François Hollande clearly did not trust the system. Why else has he reimposed border controls?

For Schengen to regain trust, the control of the common external border would have to be of the standard of the very best of the member states, not at some fudged EU average level. The EU runs an agency, Frontex, based in Warsaw, tasked with co-ordinating policy and maintaining standards. But crucially, in the Schengen area every country is responsible for maintaining its own external border controls. The external border of Greece, for example, is also part of the Schengen area's common external borders as well.

Limited job

Frontex does not have the resources even to do its limited job properly, let alone to act as a federal-level border control unit, which is what is really needed. America has the US Citizenship and Immigration Services, which are part of the Department of Homeland Security, and the US Coast Guard, which is a branch of the armed forces. In

Europe

, we rely on civil servants passing information to each other – or not, as it turned out.

The EU will tinker with Schengen, but not fix it. Sound familiar? When the euro zone crisis started, a few bold measures would have fixed it. But there was no political majority for a federal-level solution to the banking and sovereign debt crises. Why would EU leaders do the right thing for Schengen, when they failed to do it for the euro zone?

The alternative would be to allow Schengen to wither away, and to revert to national systems. This is what I expect will happen. It is not a bad option. It will work because member states have their base infrastructure still in place. It is, of course, terribly inefficient for 26 countries to operate their own intelligence networks, and to police their internal borders. The length of the borders around France and Germany alone is about 3,000km each. The external land border of the whole Schengen area is only 8,800km. If Humpty-Dumpty falls apart, there will be lot of bits and pieces, and lots of protruding edges. The internal borders would return. Before the attacks, they were almost invisible. On the train from Brussels to Paris, you would be hard pressed to notice when you changed countries. On the motorway, a derelict frontier post would have reminded you that there was once a border. Schengen turned the Molenbeek district of Brussels and Saint-Denis in northern Paris into adjacent neighbourhoods. The terrorists led the life of commuters, living in Brussels and working in Paris.

Order of magnitude

Since we are not going to fix Schengen, let us return to national border controls. It will be very expensive, especially for France, which has yet to build up a fully functional domestic security service.

It will be of an order of magnitude to derail any budget plan and will rouse the ire of euro zone bean counters. France should invoke, unilaterally if need be, the clause of an exceptional circumstance under European budget rules.

The overriding goal has to be to preserve one of the most important common goods the EU can provide to its citizens: a modern and professional level of internal security. Schengen cannot deliver this. But the member states still can, and should be allowed to do this. – (Copyright The Financial Times Limited 2015)