The Conservatives' efforts to reach out to gay voters suffered a fresh set-back after a Conservative election candidate described homosexuality as "not normal".
The party immediately denounced Philip Lardner's comments as "deeply offensive and unacceptable", suspended him from the party and disowned his candidacy.
It is the third embarrassing row over the party's attitude towards homosexuality to hit the Conservative campaign and last night there were signs that Tory support was sliding within the gay community.
Mr Lardner's political career came to a swift end after he spelt out his support on his website for Section 28, the law enacted in 1988 by the Thatcher government preventing schools from "promoting" homosexuality. Mr Cameron last year apologised for the Tories' previous support for the measure.
But Mr Lardner, who is standing in North Ayrshire and Arran, told voters: "With experience as a teacher and a believer in parental rights and responsibilities, as your MP I will support the rights of parents and teachers to refuse to have their children taught that homosexuality is 'normal' behaviour or an equal lifestyle choice to traditional marriage.
"I will always support the rights of homosexuals to be treated within concepts of [common sense] equality and respect, and defend their rights to choose to live the way they want in private, but I will not accept that their behaviour is 'normal' or encourage children to indulge in it."
His posting, under the heading "what I believe in", also asserted that most people believed homosexuality to be "somewhere between 'unfortunate' and 'simply wrong'".
Chris Bryant, the Europe Minister, who last month held the first civil partnership ceremony in the House of Commons, said the comments betrayed the "nasty, judgmental truth behind the Tory campaign".
During campaigning, Mr Cameron said he had taken action against his candidate "within minutes". He said: "I think people in the gay community know it is easier for people who are Conservative and gay to vote Conservative than at any time before.
But he conceded: "The Conservative Party has been on a journey. Has it been far enough and fast enough? Perhaps not, but it's gone further than many other parties around the world."
A survey for pinknews.co.uk suggested that support for the Conservatives among the LGBT (lesbian, gay, bisexual, transgender) community had collapsed over the last year. It found 58 per cent of LGBT voters said they intend to vote Liberal Democrat next week, compared with 21 per cent for Labour and just 9 per cent for the Tories. A similar survey ahead of last year's European elections found 39 per cent planned to vote Tory.
Almost half (49 per cent) said they wanted Nick Clegg to become Prime Minister, with 20 per cent preferring Gordon Brown and 19 per cent David Cameron .
Chris Grayling, the shadow Home Secretary, apologised over comments in which he said that people who ran bed and breakfasts in their homes should "have the right" to turn away gay couples.
And The Independent revealed last week that Julian Lewis, the shadow Defence Minister, had said the age of consent for homosexuals should not have been lowered to 16 because it put teenage boys at "serious physical risk". The party distanced itself from Mr Lewis's comments, but decided not to take action against him.
Last night Tory sources denied the party had acted inconsistently by taking tough action against Mr Lardner, insisting there was "no comparison" between the cases.
His name will remain on ballot papers as it is too late to withdraw from the election. It is also too late for the Tories to select a candidate in the Scottish constituency.