EU leaders will tackle the vexed and costly issue of defence cooperation at a summit this week, aiming for modest progress at a time when budgets everywhere are under intense pressure.

Bogged down for the last few years in efforts to tame the financial and debt crises, European Union leaders are expected to agree Thursday to joint drone and cyber-defence programmes.

That would be a minimum at a time when, for example, French intervention in the Central African Republic, the crisis in Syria and refugees from conflicts in Africa, all raise difficult questions of priorities and cost for Europe.

Opinion polls consistently show that most EU citizens would like to see the bloc adopt a more coherent and consistent policy, allowing it to intervene effectively in crises threatening its security.

But in practice, the issue goes to the heart of national sovereignty, with member states jealously guarding expensive military assets for their own use.

At best, they can agree to help in operations -- as in Libya in 2011 or in Mali last year -- by providing logistics or medical assets but not troops for common use.

Governments appear unwilling to take any risk that might compromise their national security, which has been ingrained in them as the main priority over hundreds of years.

"A common policy has never seemed so absolutely necessary but we do not see the desire, the ambition for the summit to produce real results," said Arnaud Danjean who heads the defence committee in the European Parliament.

Apart from Britain and France, no other country within the 28 members "has any appetite to take on external operations," Danjean said.

Many certainly step up when it comes to civilian missions, such as Germany, or in training as in Mali, or in anti-piracy efforts off the Horn of Africa coast but very few will go further.

Tight military budgets

The harsh reality too is that most member states have reduced spending as a result of the crisis and once cut, it is notoriously difficult to increase defence expenditure again.

Last year, EU states spent an average of 1.6 percent of Gross Domestic Product on defence -- some 190 billion euros in all -- but this compared with nearly five percent for the United States which has effectively guaranteed European security since World War II.

With the economy now just barely recovering, "it becomes difficult for any EU nation to develop ambitious military programmes on its own," said Claude-France Arnould, head of the European Defence Agency.

"The only solution is cooperation."

Against this background, EU leaders will look at a series of very targeted joint programmes in drones, satellites, air-to-air refuelling and cyber-defence.

The Libyan conflict showed up many weaknesses, forcing Britain and France to seek help from the United States, especially in drone surveillance and inflight refuelling.

As a result, seven EU states, including France, Germany and Italy, are joining forces to develop drones, aiming to have a long-range, new-generation drone in operation by 2020 which can be used for both civilian and military purposes.

Whether such projects and "a la carte cooperation" can overcome the fragmentation of Europe's armed forces remains uncertain for now.

It is estimated that the 28 member states between them operate 16 different types of frigate, compared with just the one for the United States, and 14 different tanks.