George Soros said the pound may slump more than 20 percent against the dollar if Britain votes to leave the European Union, a devaluation bigger and more disruptive than when the billionaire profited by betting against the currency in 1992.

The pound would fall by at least 15 percent and potentially more than 20 percent to below $1.15, the investor wrote in an op-ed published in the U.K.’s Guardian newspaper on Tuesday. He said voters are grossly underestimating the true costs of Brexit, which will have an “immediate and dramatic impact” on financial markets, investments and jobs.

“Too many believe that a vote to leave the EU will have no effect on their personal financial position,” Soros wrote. “This is wishful thinking. It would have at least one very clear and immediate effect that will touch every household: the value of the pound would decline precipitously.”

Governments and investors around the world are closely monitoring the June 23 referendum amid concern that a U.K. decision to leave the EU would spark turmoil across financial markets. The pound surged the most since 2008 on Monday, spurring a global rally in higher-yielding currencies, as polls signalled the campaign to remain in the EU was gaining momentum.

Soros said a large devaluation of the pound would be less benign than in 1992 because the Bank of England won’t be able to cut interest rates if voters decide to leave the EU since rates are already at low levels. The central bank will also have little room to move in the strong likelihood of a recession caused by a decline in house prices and a loss of jobs after Brexit.

Soros cited Britain’s large current account deficit, bigger than 1992 and 2008, saying the nation is more dependent than ever on foreign capital. After a Brexit, capital flows would reverse, especially during the two years of uncertainty when Britain negotiates its exit from the EU, he wrote.

Soros said a post-Brexit devaluation is unlikely to result in an improvement in manufacturing exports that was seen after 1992 because trading conditions will be too uncertain for British businesses to make new investments, hire more workers or add to export capacity.

Pound Forecasts

The day after the referendum, the pound will either sink to the lowest level in more than three decades or climb toward the highest this year, according to a Bloomberg survey of economists. In the event of a leave vote, most  forecasters saw the pound falling to a range from $1.25 to $1.40, while a decision to remain could boost the currency within its current range or beyond $1.50.

A more than 20 percent slump would result in the pound at a level that would ironically mean the currency would be worth about one euro, a method of “joining the euro” that nobody in Britain would want, Soros said.