Leading article: EU expansion depends on Ireland

This week Ireland votes for the second time on the Lisbon Treaty but with a different result expected. Adversity has humbled the once confident Celtic tiger, which threw down a gauntlet to Brussels by voting "no" in 2008. It looks a more pliant creature today. Without a dramatic change in opinion before Friday, the "yes" camp appears set to carry the day.

This will disappoint Eurosceptics in Britain and elsewhere who must be desperately hoping for a last-minute change of heart in the Republic. Another Irish "no" could scupper the Lisbon Treaty for good and throw a mighty spoke into the wheels of the EU chariot. A "yes" vote, on the other hand, leaves the Tories looking isolated in Europe in their opposition to ratification. What has been missing from the debate, however, is much discussion of how the Irish vote will affect those countries waiting to join the EU. Since 2004, when Romania and Bulgaria were admitted, the EU has thrown the equivalent of a large blanket over east and south-east Europe but with a huge hole in the middle, covering the former Yugoslavia and Albania.

Some of these states have few hopes of membership in the short term. Others, such as Croatia and Macedonia, obtained EU-candidate status years ago but cannot move forward on accession until the row over Lisbon is resolved.

There is nothing to prevent the EU from expanding eastwards if the Lisbon treaty fails to gain general assent – but it won't happen. "No expansion without Lisbon" has become a mantra in some EU countries, especially Germany.

This is unfortunate, because the continued existence of a kind of black hole to the west of the EU's eastern border with Ukraine and Turkey makes this region a magnet for traffickers. It also renders the EU's external border so complex that policing it becomes almost impossible.

An Irish "yes" on Friday will not resolve the debate over where the EU's final eastern border should lie. It will, however, help to end the current logjam which, for no good reason, has left half the Balkans in the EU, and half outside it. As the Irish vote, they must remember that the future of other countries far beyond their own lies partly in their hands.