The tripped lower on Friday on what traders called a "flash crash" that knocked the currency to a 31-year low, while the dollar slipped on news of unexpectedly weak U.S. job growth in September.
Even before a sudden plunge that briefly shaved a tenth of the pound's value during Asian trading, the sterling was on track for its worst week since January 2009 as some national leaders call for Britain to make a "hard" exit from the European Union.
"I think it's a warning shot from the markets to the UK about what type of potential volatility in sterling we may see down the line," said Shahab Jalinoos, global head of FX strategy at Credit Suisse in New York.
On Friday, the pound plunged about 10 percent from levels around $1.2600 to $1.1378 in a matter of minutes in thin early Asian trading.
Thomson Reuters later revised that low to $1.1491, which was still the weakest level for sterling since 1985. The company, which owns the Reuters foreign exchange brokerage platform RTSL, said an outlying trade had been cancelled.
Sterling retraced to $1.2391 in U.S. trading but was still down 1.8 percent on the day.
The pound pared its earlier losses as other major currencies strengthened against the dollar in reaction to a U.S. government report that showed a 156,000-job gain last month, which was below the 175,000 increase forecast among analysts polled by Reuters.
The was last down 0.2 percent at 96.554. It rose to a more than two-month high shortly before the release of the September non-farm payrolls report.