Tim Montgomerie, the editor of Conservative Home has urged Conservative Prime Minister David Cameron to argue more passionately in favour of same-sex marriage, but he warned that at present, Mr Cameron is on the “right side of history, but the wrong side of his core voters” on this issue.

Mr Montgomerie, who is also a columnist for The Times, was speaking at a gay political discussion organised by Village Drinks.

He said: “A lot of people see David Cameron as a PR guy, people see him as someone who takes a position not necessarily because he believes it but because that’s what the opinion polls suggest that he should.

“He took a position on gay marriage quite bravely five or six years ago but he hasn’t gone out on the public square and argued about it in a passionate way.

“He hasn’t gone and said why he believes in it and this is why it’s an issue deep in his heart, deep in his convictions. I think that is what we need to see from him on a lot of things. We need to see someone in the arena saying you might not agree with what I say but this is where I stand. I’d like to hear him say it on gay marriage, on some of the some of the economic issues and on Europe. But everything we’re so often seeing is very calculated and measured.”

Last year, Mr Cameron made a groundbreaking speech to the Conservative Party conference on the issue where he said: “I stood before a Conservative conference once and I said it shouldn’t matter whether commitment was between a man and a woman, a man and another man or a woman and a woman.”

He added: “So I don’t support gay marriage in spite of being a Conservative. I support gay marriage because I am a Conservative.”

The prime minister reinforced the message at an event for the LGBT community held in Downing Street in July where he said: “It’s something [marriage] I feel passionately about and I think if its good enough for straight people like me, its good enough for everybody and that’s why we should have gay marriage and we will legislate for it.”

Despite his vocal support for the policy, Mr Montgomerie used his speech to warn that David Cameron is placing himself in a precarious position over the issue of marriage equality. “It has been a huge problem for him among a lot of core Conservative voters. Opinion polls suggest that most people are in favour of gay marriage, but a lot of the people who are in favour of gay marriage are never going to vote Conservative. This has upset the minority, who are among the most reliable Conservative supporters.

“So Cameron has definitely taken a political risk that he regrets and it makes it harder for him to do other things. I think his stance is right. He’s on the right side of history but on the wrong side of a lot of his core voters. The problem for him is that winning the next election is going to be difficult anyway and the gay marriage issue has probably made it harder.”

Earlier this year, Mr Montgomerie recorded a video for the Out4Marriage campaign where he said that marriage “is an institution that builds the best in society. It’s a compassionate, caring, inclusive institution and I want as many people as possible to be part of it. That is why I’m Out4Marriage, Out4Marriage for gay people as well as for straight people.”