The pound plunged more than one percent against the dollar and euro Thursday after Britain's Brexit Secretary Dominic Raab quit over opposition to a draft deal to exit the EU.
Around 0925 GMT, the pound was worth around $1.2831, compared with almost $1.30 late Tuesday.
The euro meanwhile jumped to 88.22 pence, a gain of 1.3 percent.
"There's been a sharp move lower in the pound ... after Brexit minister Raab announced his resignation," said XTB analyst David Cheetham.
British Prime Minister Theresa May was preparing to sell her Brexit deal to parliament, boosted by news that Europe is preparing a rapid summit to sign off on the agreement.
But the ground began to shift beneath her when Raab said he could not back the deal.
The resignation "is a major blow for May and others will likely follow suit in offering their resignations with her position now growing increasingly tenuous", Cheetham said.
"It now seems probable that a vote of no confidence will be tabled, with some reports stating that the requisite 48 letters will be sent by lunchtime."
Sterling was also hit by news that official retail sales slid by 0.5 percent in October compared with September.