UKIP leader Nigel Farage said David Cameron is paying the price for being out-of-step with the Conservative Party's traditional supporters on the issue of same-sex marriage.
Following the result of three weekend polls that placed UKIP ahead of the Liberal Democrats, Mr Farage told BBC1's Sunday Politics, "It is the Conservative Party support that will suffer most from this proposal".
It wasn't in Cameron's manifesto, there was no public call to do this, and yet he is pursuing headlong a policy that is going to enormously damage and split his own party, particularly in the shires.
I think gay marriage is one of those issues where attitudes in the big metropolitan centres compared to the shires are very, very sharply different.
Mr Farage also denied that his party was homophobic and defended its alliances in the European Parliament with groups - such as the the United Poland party - which have been accused of being anti-gay.
More top news
David Cameron has revealed he has "no plans" to meet up with his thirteenth cousin .... Kim Kardashian.
Today there's a mixture of weather around, but it's the wind that has got everyone's attention after a night of howling gales.
We examine the chances of each player in England's under-21 team breaking into Roy Hodgson's plans for Euro 2016