When you have a single currency, everything must be single, argues Marinos Gialeli.

For the euro to remain the single currency for those countries belonging to the euro-zone, radical changes must be made to the European Union. It has been proven beyond any doubt that when you have a single currency, everything must be single. If the EU does not become the 'United States of Europe', if it does not adopt a single foreign policy, a single economic policy, a single monetary policy, then it will be very difficult to save the single currency - and that is because the countries facing economic difficulties cannot depreciate their currency.

Within the next few years, after considerable effort, some form of federal EU will be formed, with a single ministry of foreign and financial affairs. Furthermore, at some level, a fracture of the euro-zone will be inevitable. Up to now, economic history has taught us that, in a partnership, all participating parties must win together - if some are winning while others are losing, sooner or later, the partnership will be dissolved.

Today, Germany imposes its own terms by having a strong euro, but countries that are less dependent on exports and cannot depreciate their currencies would obviously prefer a weaker euro. These two strategies cannot continue to coexist under a common currency if a common policy does not also apply.

The road will not be an easy one, and I would even venture to say that it will indeed be a difficult one. François Hollande, who is likely to run against Nicolas Sarkozy for the French presidency in six months' time, has already warned the incumbent president that the French people will not abide losing their sovereignty.

Furthermore, while Sarkozy and German chancellor Angela Merkel appear to agree on the evolution of the EU and tough measures to be taken against countries failing to comply with their fiscal policy - with the European Commission going so far as to interfere with member states' budgets - there is a growing chorus of voices in France and other countries decrying the 'Germanisation' of the EU. The upcoming French elections in 2012 could therefore prove decisive for the euro-zone's fate.

On the one hand, we have the changes that must be made so that euro remains the single currency, while on the other hand we have the changes that must not be made so that member-states are not forced to cede some of their sovereignty. One thing is for certain: these two scenarios cannot both apply. The road ahead for a United European Union will be a very harsh one, and one that will pass through many changes, whatever those changes may ultimately be.

Marinos Gialeli is general manager of the €270m Hotel Employees Provident Fund, winner of IPE's Best Pension Fund in a Small Country award.