By about 1515 GMT, sterling had dived to a one-month low at USD 1.3122.
Earlier, the European single currency had hit a three- week pinnacle at 89.33 pence per euro.
"After Theresa May's speech at the Tory party conference on Wednesday, there are rumours that she will be asked to step down by her own party," said City Index analyst Kathleen Brooks.
"The prospect of a leaderless UK in the middle of the Brexit process, or even worse, a Prime Minister Boris (Johnson), are right to unnerve sterling traders."
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May's conference speech dominated today's newspapers, which had sympathy for her bad luck but bleak warnings about what the string of misfortunes signalled for her leadership.
The premier was hoping to use the keynote speech to reassert her authority following a dismal election showing.
However, she was interrupted by a comedian handing her a fake notice of unemployment, before succumbing to a persistent cough in front of a collapsing set.
"Sterling is coming under pressure again ... following speculation that Theresa May's position is increasingly under threat following yesterday's shambolic speech," added Oanda analyst Craig Erlam.
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