LONDON -- Europe is once again divided between East and West -- only this time the fault line runs through the European Union. The eastern members -- most notably Poland and the Baltic states -- are clinging fast to the EU in the face of Russian aggression. At the other geographic and political extreme, the United Kingdom is threatening to walk out on Europe for good. Decisions being taken today on Europe's eastern and western peripheries are likely to shape a new balance of power. It is not difficult to imagine Europe after a British withdrawal: a French-German axis in control, Russia empowered, America bypassing a now-weakened Britain, pro-EU Scotland threatening once again to leave the U.K. and England turning inward as Euroskeptics convince themselves that Britain always is strongest when alone. And, given the effects of U.K. Euroskepticism so far, no crystal ball is needed to foresee the impact on Britain of withdrawal from the EU. As former European Commission President José Manuel Barroso put it in December, "I have never seen in all my years in the European Council... a big country as isolated as Britain." Indeed, the U.K. is now a fringe player in deciding a European growth strategy; marginal to trade debates that it used to lead; and, despite being a big lender, almost irrelevant to the future of Greece. And now, though Britain was a signatory of the 1994 Budapest Memorandum guaranteeing Ukrainian independence, only France and Germany attend any serious negotiations. British ministers want it both ways: "Russia must be countered by even greater European unity," they say. "But, by the way, we may be leaving." Dean Acheson, the U.S. secretary of state who was an architect of NATO and the Marshall Plan, famously noted that Britain in the 20th century lost an empire and never found a new international role. In the 21st century, Britain could lose Europe and find itself once again without a role in the world. The price of exit would be enormous, putting at risk three million jobs, 25,000 companies, annual exports worth £200 billion ($301.4 billion) and £450 billion of inward investment. Moreover, London's unique role in bringing together the full range of financial services that serve the continent -- the city is home to 250 global banks with 160,000 employees and accounts for 80 percent of Europe's hedge funds, 78 percent of its foreign exchange trades, 74 percent of its derivatives and 57 percent of its private equity -- would be jeopardized as well. There is little evidence to support the anti-Europeans' argument that EU regulations hobble British trade outside of Europe; on the contrary, substantial extra-EU trade and investment opportunities would be lost were Britain to leave. And their claim that a non-European Britain could effortlessly retain the EU's benefits while ditching its burdens is simply not credible. Consider the Euroskeptics' favorite examples, Norway and Switzerland. The Norwegians must pay €2 billion ($2.1 billion) a year for access to European markets. Switzerland, like Norway, must take a back seat to the EU Commission when trade and investment decisions are made. The world's largest economy, the United States, needs the North American Free Trade Agreement, and Southeast Asia's rising economies need ASEAN. Likewise, Britain -- which at its peak generated nearly 20 percent of world economic activity but soon will account for no more than 2.5 percent -- is much stronger as a part of Europe. EU membership strengthens the U.K.'s competitiveness by enabling it to negotiate the best deals on trade, tax rules, patents, money laundering, corruption and security with China, India and the rest of the world. But economic arguments alone will likely not be enough to persuade a Britain that, in the late journalist and political columnist Hugo Young's words, is caught between the past it cannot forget and the future it cannot avoid. According to this view, British ambivalence toward Europe may reflect a persistent inability to leave behind the days of imperial grandeur. Nonetheless, economic insecurity -- owing to the rapid pace and, at times, destructiveness of the global economy -- evidently is driving much of the public's nostalgia for British sovereignty. Millions of Britons long for someone or something to protect them from the seemingly alien forces that threaten to steal their livelihoods. This fear has found its voice in the anti-European U.K. Independence Party, which has risen in opinion polls by converting economic discontent into a culture war in which foreigners and immigrants -- and, indeed, Europe as a whole -- are the enemy. Britain, UKIP's leaders and supporters believe, is not the Britain they once knew. Though economic statistics must be part of the argument for Europe, such data will not convince those who fear that Britain is becoming a foreign country. Nor will it be enough to recall the historic benefits of engagement and Britain's distinguished centuries-old role in ensuring that no country ever gained sole mastery of Europe. What needs to be said is this: Britain is at its best when it sees itself as a leader in Europe. Just as Britain once led Europe in fighting fascism, supporting democratic aspirations and charting the continent's response to the global recession of 2008, it should be inside Europe leading from the front ranks. The Britain that has always championed liberty, tolerance and social responsibility should be ready once again to lead a progressive movement, spearheading action to fight climate change, resist protectionism and encourage sustainable growth. It must lead in mobilizing Europe to make the global economy work for people, protecting them from injustice and inequity. Globalization needs a human face, and the face of modern Britain can provide it. Some say that the best way to secure European reform is to threaten to leave. My experience is that Britain does best when it works to bring people together, set the agenda, promote its values and champion change. It is then that Britain can channel its unforgettable past while embracing its unavoidable future. © Project Syndicate