Ontario public broadcaster TVO is launching an independent third-party investigation of a sexual-harassment allegation made against Steve Paikin, host of the current affairs show The Agenda.

The allegation was made by Sarah Thomson, a former candidate for mayor of Toronto. But the channel said that, based on the evidence it has so far, Mr. Paikin will remain on the air pending the results of the probe.

TVO chief executive officer Lisa de Wilde issued a statement on Monday disclosing that Ms. Thomson had published details of an incident on her website – without using Mr. Paikin's name. When she also sent him an e-mail over the weekend, Mr. Paikin immediately notified TVO, the statement said.

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According to the account of the incident on Ms. Thomson's website, while at a lunch at midtown Toronto restaurant Grano in 2010, Mr. Paikin allegedly asked if she would have sex with him in exchange for an appearance on his show. Ms. Thomson says her executive assistant, whom she did not name, was also present and that the TV host later told him the tactic worked "50 per cent of the time."

"TVO does not tolerate sexual harassment. We believe it is important that allegations be fully heard and investigated," Ms. de Wilde's statement read. "However, based on the evidence to date, TVO sees no reason to remove Mr. Paikin from his role as host for The Agenda pending the outcome of the investigation."

TVO said that during the investigation, which will be conducted by an employment-law firm, stories related to "this subject matter" will be handled by others. Mr. Paikin has been covering the chaos in the Progressive Conservative Party of Ontario that erupted after leader Patrick Brown was forced to step down amid allegations of sexual misconduct. He will be allowed to cover the leadership race.

A source close to TVO says the channel has received no other such complaints about Mr. Paikin, who has hosted current affairs programs since the early 1990s.

Ms. Thomson, a businesswoman who founded the Women's Post magazine, ran for mayor in 2010, but dropped out right before the election, which was won by Rob Ford. She later alleged that an inebriated Mr. Ford grabbed her buttocks and made a sexual comment at a 2013 gala. He denied it.

In a post on her website on Friday, she alleges that during a lunch with an unnamed TV host during the 2010 campaign, she asked how she could get on his show again: "Not five minutes into the lunch, the host asked me if I would sleep with him."

She also alleges he has approached her at other events since and repeated his remark with laughter. In her account, Ms. Thomson says she also told her unnamed campaign manager about the incident immediately. "My manager was at first angry that I was alone with a talk-show host, but when I explained that my assistant was actually sitting there with us and had heard the entire thing, his anger turned to shock. He was great at calming me down and joked that if I didn't want to 'take one for the team' then I should excuse myself and leave."

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According to a Globe and Mail report at the time, Ms. Thomson's campaign manager Wendy Stewart quit in late June, 2010. John Tory Jr., a son of Toronto's current mayor, stepped in to act as Ms. Thomson's spokesman. His brother, lawyer George Tory, was then appointed as her campaign manager that August. Reached by e-mail on Monday, neither could recall the alleged incident.

"I have no knowledge of any such incidents other than what I have read in the news today," George Tory said. "It was more than likely a different campaign manager referenced as there were more than one."

In an e-mail, Mr. Paikin declined to comment, referring inquiries to TVO. "Trust me, I'd love nothing more than to comment," he said.

Ms. Thomson did not respond to messages.

In an e-mail she sent to Mr. Paikin over the weekend and obtained by The Globe, she said she is gathering letters from other women with "similar experiences of you" and that a letter from her and from her assistant would be sent to TVO's board and CEO next month. The Globe could not independently verify the e-mail or its allegations.

The e-mail stated that using "your position to try to get women to have sex with you is wrong on EVERY level – and you should not have that kind of power over women."

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The e-mail went on to warn him to quit before the allegations went public: "My advice to you is to step down now, before this blows up. That is the right thing to do."