Britain's pound currency plunged in value against the dollar Monday after London Mayor Boris Johnson dramatically defected to the campaign for Britain to leave the European Union, NBC News reported.
The high-profile announcement dealt a serious blow to Prime Minister David Cameron ahead of the June 23 referendum that could see Britain vote to exit the trading bloc.
It was followed by a string of similar announcements by other senior ministers in Cameron's Conservative government, adding to fears that a so-called "Brexit" is now a real risk.
"I think there is genuine worry that Britain might vote to leave and the uncertainty is going to rise into the referendum," Alvin Tan, a strategist with French bank Societe Generale in London, told Reuters.
The pound fell nearly 2 percent at one point to a one-month low of $1.4133, putting it on track for its biggest daily percentage loss since May 2010.
It also fell sharply in early trading against the euro, underscoring jitters about a referendum that polls suggest could be a close-fought battle.