Zac Goldsmith's controversial campaign tactics in the London mayoral race were a "mistake" and could damage community relations in the capital, a senior Tory has warned.
The Conservative mayoral candidate and Prime Minister David Cameron sought to link Labour candidate Sadiq Khan with Muslim "extremists" in the bitter race to succeed Boris Johnson in City Hall.
But Andrew Boff, the Conservative group leader on the Greater London Assembly, launched a devastating attack on the way Mr Goldsmith's campaign was run.
Meanwhile a Labour source Mr Khan's team was "optimistic" about his chances but did not believe the large opinion poll leads he had been getting.
Mr Boff said the campaign had "done real damage" and had "blown up" bridges the Conservative Party had built with London's Muslim communities.
"I mentioned that I thought this was a mistake for future integration in London. If you are a London politician this is just a bizarre thing to do," he said.
He told BBC's Newsnight it was an error to "equate people of conservative religious views with sympathising with terrorism" but said it was not an example of so-called dog whistle politics because it was such a prominent part of the campaign.
"I don't think it was dog whistle because you can't hear a dog whistle - everybody could hear this," he said.
"It was effectively saying that people of conservative religious views are not to be trusted and you shouldn't share a platform with them. That's outrageous."
Mr Boff said the Tories had done well where they had actively engaged with the Muslim community in the borough of Newham, but "now those bridges that have been built, a few of them have been blown up by this campaign".
He said there were policy areas where the Tories could have challenged Mr Khan - but instead they focused on the extremist issue, which could have damaged the Tory chances in the London Assembly elections.
"It was ridiculous," said Mr Boff, who ran against Mr Goldsmith for the Tory nomination.
"I do believe it's going to affect Conservatives at the sharp end, especially in those parts of London where there is a high Muslim population."
Mr Khan is the bookmakers' favourite to win the mayoral race, but his team remained cautious ahead of the count on Friday.
A source in Mr Khan's camp said: "So far as we can tell, things have gone pretty much as we expected.
"Nothing has happened to move our market one way or the other.
"We are optimistic but simply do not believe the big leads we have been getting in the opinion polls."
Labour is still scarred by the shock of the general election defeat, which followed opinion polls putting the party neck-and-neck with the Tories, and the source said Mr Khan's camp was "massively cautious" as a result.