Close to two thirds of Tory councillors believe redefining marriage will be a vote loser at the next election, a new poll shows.
And reports from local Conservative associations show a rapid decline in membership, with gay marriage seen as one of the reasons.
The ComRes survey for BBC Sunday Politics showed that 63% of Conservative councillors believe legalising gay marriage will cost the Party more votes than it gains at the next election.
That is compared with 18% who disagree and say the move is a vote winner.
The poll surveyed 1,444 Conservative councillors between 22 August and 6 September this year.
In the local elections earlier this year, the Party lost more than 300 county council seats as predicted by the Coalition for Marriage.
The group’s survey ahead of May’s local elections showed that the Conservatives would lose hundreds of seats over redefining marriage.
Election expert Professor John Curtice said UKIP, which saw a dramatic increase in support at the local elections, gained support from voters who are socially conservative on issues like gay marriage.
Membership of the Conservative Party has almost halved to 134,000 since 2005.
In reaction to decreasing membership shown in local association reports, chairman of Conservative Grassroots Robert Woollard said members are leaving because they are “not seeing Tory policies”.
He said: “The way the same-sex marriage legislation was handled really upset a lot of people.”
At the weekend, it was revealed that David Cameron confided in an ally that he wouldn’t have pushed through gay marriage if he had known what the reaction would be.
He now denies regretting the legislation, saying he admits he didn’t expect such a “furore” but is passionate about marriage and thinks it should be available to “people who are gay as well as those of us who aren’t”.