Global political leaders are scrambling to send a message out. They have been in almost unison in underscoring the challenges Great Britain may face once it decides to leave the EU. The British national referendum is just three weeks away, to be held on June 23. Polls indicate that the outcome is too close to call.

The pro-remain group in the United Kingdom points to the economic damage that it says will result from the departure. Statistics put a possible British economic loss as a result of the Brexit at 6.2 percent GDP decrease by 2030, compared to what it would be if the U.K. stayed in the EU.

Upon departure, the U.K. will not be able to enjoy zero tariffs anymore for intra-EU trade and trade with other EU FTA partners, and the resulting extra-payment of duties by British manufacturers is expected to reach $8 billion annually. In order to enjoy zero tariffs, the U.K. will have to secure its own trade deals with these other countries, which is anything but easy. The departure will be costly, at least for the time being. Those supporting Brexit, however, describe the initial cost as a payment to regain national sovereignty from Brussels and the European Court of Justice. To them, initial loss will turn out to be a gain in the end.

All advice and admonition from sages are meant for the ears of Britons, basically telling them how much they would lose in terms of dollars and cents after the break-up. Accurate prediction of a long-term loss or gain is hard to come by, since, as some people say, a short-term loss will be covered by a long-term gain or vice versa. You never know in this volatile world.

It is the systemic implication of the departure that is more meaningful and grave. If the U.K.’s departure means “we are better off alone,” it may have other countries pause to think about the benefits and consequences of economic integration. In the face of the continuing economic slowdown and migration crisis, the idea of strong integration has not been popular in domestic U.K. politics.

Since its creation in 1957 with six countries, the EU has expanded continuously, reaching 28 member states now. The suggestion that someone can actually leave the entity has rarely been considered. Enlargement has been the only word in the EU dictionary so far. If the U.K. decides to leave the EU, this will be the first case of back paddling from the entity. And back paddling by an important member of the entity.

Britain’s departure from the EU means that the trade deals done under the umbrella of EU will have to be adjusted as well, together with new stand-alone deals with the U.K. The EU’s recent FTAs including the one with Korea are slightly different. In these FTAs, both the EU and the individual member states are jointly parties to the treaties. So, with respect to them a British departure would mean separation or succession of existing treaties rather than termination of treaties for a particular constituent party leaving the collective entity. In any event, a series of complex legal issues and re-adjustment of existing treaties and agreements will become inevitable.

The U.K. had a similar referendum in June 1975 to decide whether to remain in the then EEC. Almost 67 percent of voters at that time supported the continued membership. The upcoming vote this time is indeed close by any measurement. More than anything else, the British departure would presage a restructuring of the European regime established and developed after World War II.

By Lee Jae-min

Lee Jae-min is a professor of law at Seoul National University. -- Ed.