The British were warned for weeks that a vote to leave the European Union would result in economic pain. Now they will find out whether it will. U.K. financial leaders are scrambling to reassure households, businesses and investors that they can contain the doom and gloom they had predicted in case of a British exit, or Brexit. The pound plunged to its lowest level in over 30 years on Friday, raising concerns about price inflation, and shares in the U.K.'s biggest banks and real estate builders posted double-digit declines as economists predicted the country would fall into recession.

Economists slashed their forecasts for Britain, with some expecting a recession and next to no growth next year. That's a sharp reverse for an economy that had been among the best-performing in the developed world in recent years.

In an early sign of problems, Moody's Investors Service downgraded the U.K. outlook from "stable" to "negative." The referendum result, it said, "will herald a prolonged period of uncertainty for the UK, with negative implications for the country's medium-term growth outlook."

The British economy could also find it more costly to raise money. Ratings agency Standard & Poor's is considering downgrading the country because of the uncertainty related to the vote. A lower rating could mean higher borrowing costs for the government — and in the longer term, less money to spend on schools, hospitals and roads. "The real question now is how badly the EU will punish the U.K. for this decision," said Megan Greene, chief economist at Manulife Asset Management.