The pound struggled to gain ground against the dollar and the euro on Thursday due to mounting uncertainty over Brexit even as investors strengthened bets on a Bank of England interest rate hike next week.
With just over eight months left until Britain is due to leave the European Union, there is little clarity about how trade will flow as Prime Minister Theresa May tries to strike a deal with the bloc.
May on Thursday sought to reassure the public about government plans to stockpile medicines and blood products ahead of a possible no-deal Brexit.
The pound rose to as high as $1.3213 against a broadly weaker dollar, its strongest level since July 17, but gave up gains and fell into the red. It was trading down 0.1 percent at $1.3180 at 0825 GMT.
Sterling, which has been much less volatile against the euro, was virtually unchanged versus the single currency at 88.91 pence.