LONDON -- British Prime Minister Boris Johnson faced new questions Monday about his relationship with an American businesswoman who allegedly received favours and public funds while Johnson was the mayor of London.

Johnson's speech Monday to U.K. business leaders ahead of Britain's Dec. 12 general election was overshadowed by tech entrepreneur Jennifer Arcuri, who accused the prime minister of discarding her "like some fleeting one-night stand" amid a media storm about their relationship.

A U.K. police watchdog is investigating claims that Johnson gave special treatment to Arcuri while he was mayor of London between 2008 and 2016. The Sunday Times reported in September that Arcuri was given financial grants and privileged access to trade missions to the United States, Israel and Asia that Johnson led as mayor.

Johnson has insisted that "everything was done with full propriety."

In a series of U.K. media interviews, 34-year-old Arcuri said she had a "very special" relationship with Johnson lasting several years. Johnson, now 55, was married at the time.

"It was not just a sexual intention," Arcuri told the BBC. "He actually was very intrigued by my energy."

She accused the prime minister of ignoring her when she tried to contact him about how to handle the media fallout from the allegations. Speaking to broadcaster ITV, Arcuri said Johnson has now cast her aside "like some gremlin."

"I've kept your secrets, and I've been your friend," she said. "And I don't understand why you've blocked me and ignored me as if I was some fleeting one-night stand or some girl that you picked up at a bar because I wasn't. And you know that."

The Arcuri allegations erupted again as Johnson and the leaders of two opposition parties made their election pitches to business leaders, who are skeptical of politicians' promises after years of economic uncertainty over Brexit.

Britain's stalled departure from the European Union is the overriding issue in campaigning for the Dec. 12 election, which is being held more than two years early because Johnson is seeking to get a majority of lawmakers to pass his divorce deal with the EU. All 650 seats in the House of Commons are up for grabs.

More than three years after the U.K. voted to leave the 28-nation bloc, the terms of the country's departure and the nature of its future relationship with the EU remain unclear.

The election pits Johnson's Conservatives -- with their promise to "get Brexit done" -- against the main opposition Labour Party led by Jeremy Corbyn, which says it will hold a new referendum on whether to remain in the EU or leave the bloc.

Smaller parties running include the pro-EU Liberal Democrats, who want to cancel Brexit; the Scottish National Party, which seeks Scotland's independence from the U.K.; and the anti-EU Brexit Party led by Nigel Farage.

On Monday, the Liberal Democrats and the SNP lost a legal attempt to gain a place in a televised election debate between Johnson and Corbyn. The parties argued that their exclusion from Tuesday's ITV program was unlawful because it breached broadcasting impartiality rules.

But two High Court judges ruled that the debate format was a matter of "editorial judgment."

Addressing a conference of employers' group the Confederation of British Industry on Monday, Johnson promised to lead Britain out of the EU on the scheduled date of Jan. 31, saying that doing so will end the uncertainty that has weighed on business investment and confidence.

"The worst thing now is the continuing economic uncertainty: people waiting to take on new staff, or invest in property, or just to invest in this country," Johnson told the CBI conference.

He did not mention that Britain's departure will be followed by many months -- and potentially many years -- of negotiations with the EU on a future economic relationship.

Johnson also promised to cut a tax paid by businesses with bricks-and-mortar premises but announced plans to postpone a reduction in the corporation tax, which had been due to fall from 19% to 17% next year.

Johnson said putting the cut on hold was "the fiscally responsible thing to do" and would allow more investment in the country's publicly funded National Health Service.

At the same conference, Corbyn pledged a major expansion of apprenticeships and said a Labour government would crack down on "tax tricks" used by wealthy individuals and corporations.

Some businesses are alarmed by Labour's economic plans, which call for a greater role for the state in key industries. Last week the party said it backed a plan to part-nationalize telecoms provider BT and provide free internet access to all Britons.

Corbyn said he understood businesses' "caution" about Labour's plans.

"But your businesses, your workers, your consumers have been failed by rip-off energy bills and very poor rail and bus services in many parts of the country. And I think many of you know that, because you know things can't go on as they are," he said.

Swinson, whose party currently holds just 20 seats in the House of Commons, argued that her centrist Liberal Democrats are the "natural party of business" because they want Britain to remain in the EU. That view is shared by many industries eager to retain access to the bloc's huge single market of over half a billion people.

Businesses, meanwhile, are wary of all sides. CBI Director-General Carolyn Fairbairn criticized both hard-core Brexiteers seeking "the wholesale deregulation of the U.K. economy" and Labour's left-wing plans to nationalize big chunks of the economy.

"These ideologies from both sides are causing great harm to our economy. Not just in the future but right now," she said.