Polls increasingly favor Great Britain's exit (aka "Brexit") from the European Union, which would clobber the nation's economy and currency, but investors can make a quick killing from Britons' imminent folly.

During its apogee in the late 19th and early 20th centuries, the British Empire reached a territorial size larger than that of any other empire in history. Britain was once referred to as "the empire on which the sun never sets."

But someone forgot to tell the United Kingdom that its empire is largely gone. Rising nationalism, fear of immigrants and the lingering pride of British "exceptionalism" are driving this island nation to the brink of abandoning the EU.

Now, the sun is about to set on the country's economy.

A referendum on the country's membership in the EU is scheduled for June 23. Despite the entreaties of Prime Minister David Cameron and the British business community, the latest polls this month show that the "leave camp" enjoys a 9-point lead.

To appease those in favor of leaving the EU, this month he negotiated a new settlement with EU leaders that grant the United Kingdom several modest concessions, including more autonomy and restrictions on immigration. However, increasingly restive euro skeptics in Cameron's Conservative Party have branded the deal a joke, and they vow to press ahead on leaving the EU.

Exacerbating Brexit fervor is the country's growing right-wing populism, fueled by fears of recession, terrorism and refugees. Xenophobia is on the rise elsewhere in the world, as the strident rhetoric of this year's presidential race in America shows.

As the finance ministers and central bankers from the world's leading economies or the Group of 20 gather this week in Shanghai, China, the likely turmoil wrought by Brexit is high on the agenda.

The analyst consensus is that Brexit would hammer the value of the British pound, with extreme volatility leading up to the actual referendum vote.

Currency experts at Goldman Sachs recently declared that "an abrupt and total interruption to incoming capital flows in response to a 'Brexit' could see the pound decline by as much as 15% to 20%."

In a forecast this week, HSBC warned that the pound could fall by 15% in the wake of Brexit. The global investment bank also warned that the pound's decline could drive up the country's inflation rate by as much as 5% and slash Britain's economic growth by up to 1.5%.

A Brexit vote would weigh on the value of pound sterling as investors abandoned the British asset, at least until the scope of the economic damage of leaving the EU could be assessed. It would also impede the free flow of capital in London's banking sector and hit the balance sheets of specific banks such as Royal Bank of Scotland, as their U.K.-based corporate clients grapple with greater uncertainty and lost business.

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The United Kingdom's £229 billion annual trade with the EU would take a hit because Brexit would result in new trade barriers and tariffs. One of the key benefits of EU membership is free trade among member nations, which makes exporting goods to other EU countries cheaper and easier for British companies.

Britain's gross domestic product would likely suffer under Brexit because stricter export conditions would dampen certain sectors, especially retail and London's vital financial services industry. British stocks, in turn, could tank.

The best way to play the trend is to short the CurrencyShares British Pound Sterling Trust (FXB) - Get Report , an exchange-traded fund that seeks to track the price of the British Pound Sterling.

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FXB data by YCharts

With net assets of $55.54 million, the ETF has an expense ratio of 0.40%. FXB is the most popular ETF pegged to the pound and has a trading volume trades of about 16,000 shares a day.

The fund is down more than 5% year to date.

By shorting the pound, investors will be following famous historical precedent. Billionaire super-investor George Soros is known as "The Man Who Broke the Bank of England" because of his short sale of $10 billion worth of British pounds, reaping him a profit of more than $1 billion during the 1992 "Black Wednesday" currency crisis in the United Kingdom.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.