Labour Party leader Jeremy Corbyn said he would join a multiparty debate organized by the BBC in Cambridge on Wednesday. May has refused to do any live TV debates, and Corbyn had previously said he would not take part without her. But buoyed by rising poll ratings and the chance to make May look evasive Corbyn changed his mind.
"I invite her to go to Cambridge and debate her policies, debate their record, debate their plans, debate their proposals and let the public make up their mind," he said.
At a campaign rally in southwest England, May denied she was running scared.
"I've been taking Jeremy Corbyn on directly week in and week out at Prime Minister's Questions" in the House of Commons, she said.
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"I think debates where the politicians are squabbling amongst themselves doesn't do anything for the process of electioneering."
May called a snap parliamentary election for June 8 three years early arguing that a bigger majority for her Conservatives will strengthen Britain's hand in Brexit negotiations with the European Union.
The pound fell below $1.28 Wednesday, its lowest level in more than a month, after pollster YouGov suggested Britain could be headed for a hung Parliament in which no party has an overall majority.
YouGov stressed that was just one possible result of its research, which is based on a mix of polling and demographic modeling.
But it follows a trend.
But he said the outcome of the election was now in doubt. "We can't be sure Theresa May is going to achieve her political objective of a landslide majority," he said. "We don't know whether she is going to achieve her original ambition in calling this election or not. That's what's changed.