Hedge fund magnate George Soros, who earned more than a billion dollars when he bet against the British pound sterling in 1992, is warning that a British vote on Thursday to leave the European Union would spark a “black Friday” and leave voters “considerably poorer.”

Soros, writing in an opinion piece in the Guardian newspaper, said a so-called Brexit would trigger a bigger and more disruptive sterling devaluation than Britain’s Black Wednesday in September 1992. The British government that year was forced to withdraw its currency from the European Exchange Rate Mechanism after it was unable to keep the pound from dipping below a mandatory minimum level.

Soros had been building a large short position in pounds, betting that the currency would eventually drop below its minimum requirement. The Hungarian-born American investor profited around $1.5 billion and broke the Bank of England after the currency plunged by 15 percent.

That ill-fated Wednesday in 1992 cost the British economy about 3.3 billion pounds ($4.85 billion), according to U.K. Treasury papers previously obtained by the Guardian. Soros this week said a Brexit from the European Union would have far more devastating effects for British residents.

He said sterling is “almost certain to fall steeply and quickly” if the "leave" campaign wins the June 23 referendum. The pound could fall by at least 15 percent, and possibly more than 20 percent, to below $1.15 against the U.S. dollar from its current level of about $1.46, he speculated.

Soros, whose net worth is estimated at $24.9 billion, said he did not expect the Bank of England to cut interest rates after a Brexit and that the government would have few monetary policy tools left to stave off a recession of a drop in British house prices.

“Too many believe that a vote to leave will have no effect on their personal financial positions. This is wishful thinking,” Soros wrote in the Guardian. “If Britain leaves the EU it will have at least one very clear and immediate effect that will touch every household: the value of the pound would decline ­precipitously. A vote to leave the EU would also have an immediate and dramatic impact on financial markets, investment, prices and jobs.

“A vote to leave could see the week end with a black Friday and serious consequences for ordinary people,” Soros added.