David Cameron’s (pictured) plan to introduce same-sex marriage may be still on track, but it has already brought deep fissures within his own party to the surface, and these divisions are only set to grow.

He has been forced to grant his MPs a free vote, but that has not quelled the rebellion. Many Tory MPs and rank and file members are furious that the Prime Minister is pressing ahead with plans to redefine marriage, especially given the fact that it was not a manifesto committment.

Charles Moore, writing in the Daily Telegraph, said that Mr Cameron “has annoyed his grassroots supporters more by his backing for same-sex marriage than by anything else he has ever done”.

He writes: “Most of them are against it in principle and bewildered about why their leader thinks it urgent. Conservative MPs, including some in favour of the change, tell me that they haven’t encountered such resistance and such upset on any issue since he took over in 2005.”

Moore says that Cameron’s move will alienate the party activists who campaign for MPs up and down the country. He maintains that the move is “unconservative” and argues that “When Conservatives forget how to be conservative, they end up losing.”

Moore admits that he is opposed to same-sex marriage, but Mark Hennessy, London correspondent for the Irish Times, who doesn’t state his view, also sees political trouble for Cameron.

According to Hennessy, while same-sex marriage is certain to pass the House of Commons (since it will be supported by Labour and the Liberal Democrats) “it is far from certain that it will be passed with a majority of his own people”.

Hennessy compares Cameron’s difficulties on this issue with the problems faced by Tony Blair in 2006 over education reform.

“In 2006, Tony Blair had to rely on the then newly arrived Conservative leader (Mr Cameron) to get some of his education reforms past angry Labour MPs.

“Blair won that night, but it could be argued that his authority over his own was never the same.”

Hennessy also makes the point that while there is majority public support for same-sex marriage in the UK, “a significant percentage of this group is ‘soft’”.

Such support, he suggests, might not disappear but the many of the voters who back same-sex marriage, “do not feel so strongly about that they will reward the man who brings it about”

However, “many people are strongly opposed to gay marriage, and they may well punish such a figure. If they are Conservative, there is a danger that some will migrate to the UK Independence Party , which is posing an ever bigger danger to the Conservatives”.

The lesson of all this, especially for a conservative party, is that there is very little political margin in supporting same-sex marriage. Most of the people who are strongly in favour will likely not vote for you anyway, and you end up alienating the voters and supporters that put you in power in the first place.

Food for thought for Fine Gael, perhaps?