12/12/2012 04:26 GMT | Updated 10/02/2013 05:12 GMT

Gay Marriage is Retoxifying Not Detoxifying the Conservative Party

David Cameron's backing of gay marriage was meant to be an easy way to cement the detoxification of the Tory brand. However the most striking memory of debate is more likely to be a Tory MP claiming that he couldn't possibly be a bigot because he once punched a gay man in the face.

Culture secretary Maria Miller's encounter with Tory MPs on Monday and Tuesday saw Conservatives line up not only to attack the plan, but compare gay marriage to polygamy and dismiss it as not "normal". One suggested that straight couples would be more likely to have babies out of wedlock if gay people were allowed to tie the knot - because, presumably, the very institution of marriage would then have gay germs on it.

Same-sex marriage was described by one Conservative as "a constitutional outrage and a disgrace", another was "deeply offended", his colleague said plans for equal marriage smacked of "arrogance and intolerance" and another was concerned "this country will be passing a law that is directly contrary to what Jesus said".

Over half the Tory parliamentary party is expected to vote in favour of gay marriage. However their support, from the begrudging to the sincerely enthusiastic, is drowned out by the large number of their colleagues who will vote noisily against.

David Davies, the MP who inexplicably submitted a video of him boxing a gay guy as evidence of his lack of bigotry, was trying to undo damage done by insisting that most parents would not want their children to be gay. And Conservative Bob Blackman called for the re-introduction of the anti-gay Section 28 law.

Cameron is right to introduce gay marriage. It is the correct thing to do and he should be applauded. And helpfully, according to Ipsos-MORI, 73% of the public also supports it.

The passage of gay marriage legislation was designed to show how the Tory party had changed. Instead it looks more likely it will demonstrate how in large part, it has not. Perversely, and frustratingly for the prime minister, rather than detoxifying the Tory brand, triggering a debate about gay marriage has retoxified it.

The Bill due to be introduced in January should have no trouble passing the Commons given the support of Ed Miliband and Nick Clegg. However over 100 Tory MPs plan to vote against the Bill. The prime minister will not be able to argue he has detoxified his party if he is only able to introduce gay marriage thanks to the votes of Labour and Lib Dem MPs.

In just over two hours of Commons discussion on the issue, backbench Conservatives have generated multiple 'anti-gay Tory' headlines. When the Bill is introduced there will be many more hours of debate, generating countless more toxic headlines. And when the voters look at the record of the Tories, Labour and the Lib Dems on gay rights, they won't side with the one whose leader let his MPs repeatedly [metaphorically] punch gay guys in the face to prove he wasn't homophobic.