The Conservative Party will not investigate a sexual assault allegation levelled at one of its London mayoral hopefuls, party sources have told Sky News.

Former Downing Street adviser Daniel Korski has denied “in the strongest possible terms” an accusation from TV producer Daisy Goodwin that he groped her.

But a source within the party said no official complaint had been made, meaning they could not launch a probe, and there were not thought to be any witnesses.

However, a senior Conservative who was backing Mr Korski told Sky News: “This feels unsustainable, and if I were advising him, I would say pull out of the race, and quickly.”

In an article for The Times, Ms Goodwin alleged she was “groped” by Mr Korski a decade ago when he was working as an adviser to then Prime Minister David Cameron.

She said she did not feel “frightened” at the time, and that she was “older, taller and very possibly wiser” than him.

Ms Goodwin said the #MeToo movement encouraged her to share her story without naming Mr Korski – but now he was running for public office, she wanted to publicise the alleged encounter.

In response, a spokesman for Mr Korski said: “In the strongest possible terms, Dan categorically denies any allegation of inappropriate behaviour whatsoever.”

Mr Korski was Mr Cameron’s deputy head of policy between 2013 and 2016, before working on the Remain side of the Brexit debate.

A series of hustings are taking place in the race to be the Conservative candidate for mayor of London.

Tory members will vote from 4-18 July on their preferred choice, with the winner announced on 19 July.

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