A decision by the United Kingdom to exit the European Union would likely trigger a big sell-off in the pound, a sharp decline in household income and a recession, according to billionaire investor George Soros.
Just ahead of the vote by Britons on Thursday on whether to exit the EU or remain, Soros issued an urgent warning about potential consequences.
"Too many believe that a vote to leave the EU will have no effect on their personal financial position," Soros wrote in an op-ed Tuesday in The Guardian newspaper. "This is wishful thinking."
Citing estimates from multiple authorities including the Bank of England and the International Monetary Fund, Soros said the average income loss per household due to a falling British currency would be £3,000 to £5,000 annually ($4,400 to $7,335).
Soros understands fluctuations in the British currency — he made a good chunk of his fortune betting against the pound in 1992. Now, he is predicting that a Brexit would cause a 15 to 20 percent decline in the currency.
While the 1992 tumble ended up aiding the country in the long run, as it brought down interest rates and helped ignite a recovery, Soros said a devaluation would not be healthy this time.
He cited three reasons: The Bank of England could not cut rates from already low levels; the U.K. has a large current account deficit and likely would not see another inflow of cash; and the loss of currency value wouldn't help exports, because of uncertainty in trading conditions that the Brexit would trigger.
"I want people to know what the consequences of leaving the EU would be before they cast their votes, rather than after," Soros wrote. "A vote to leave could see the week end with a Black Friday, and serious consequences for ordinary people."
Wilbur Ross, chairman at W.L. Ross & Co., said there are "tremendous amounts" of short positions against the pound that would moderate any currency decline in the event of Brexit.
"I think George may be exaggerating a little bit when he says 15 to 20 percent. That would be an astonishing move for any currency," he told CNBC's "Squawk Box" on Tuesday.
Richard Turnill, global chief investment strategist at BlackRock, said Soros' call represents the extreme end, but a double-digit decline in the pound is indeed plausible.
In Turnill's view, the pound could also see a double-digit upside move in the event of a "remain" vote as large short positions unwind.
"Just think, you've seen this week [the pound] move from 1.41 to 1.47 purely on about a 10-point swing in the prediction markets. If that goes to 100 percent probability, you could easily see a larger move," he told "Squawk Box" on Tuesday.