From the official website:

The Prime Minister is deliberately provoking a conflict with people of faith, and risking turning their beliefs into criminal 'hate offences', by pursuing the legal enforcement of same-sex marriage, according to UKIP.
The party's National Executive confirmed that while UKIP fully supports the concept of civil partnerships, it opposes the move to legislate for same-sex marriage.
NEC member and the party's appointed spokesman on the subject, David Coburn, said: "We are a libertarian party which doesn't believe in the government interfering in how people live their lives. We support civil partnerships, enabling gay men and women to register their long-term commitment to each other. I have fought for this all my life.

"But David Cameron seems to be saying that marriage is something else. If so, it is clearly in the domain of the church and other faiths – and it is none of government's business to meddle with it.

"It seems that, through some kind of political correctness, David Cameron is picking a fight with the millions of people whose religious faiths do not recognise same-sex marriages. That, in our view, is an aggressive attack on people of faith, and an act of intolerance in itself.

"In addition, if the government does legislate in this way, we believe that any criticism of same-sex marriage which may be expressed by someone on the basis of their faith could be classified as a 'hate crime'. That would be a grotesque assault on people's freedom of conscience."