Would extending civil partnerships to heterosexual couples "undermine the sanctity of marriage"? It's a real risk, according to David Cameron, if we are to believe reports in the Sunday Times that the prime minister intends to veto such proposals in direct opposition to Clegg and the Liberal Democrats. How exactly it would do that is unclear, of course – civil partnerships were set up so that the government at the time could have its cake and eat it on the issue of equal marriage, claiming that they had achieved it while actually creating something different. The two institutions were supposed to be distinct enough that there wouldn't be any sanctity-ruining crossover between them – but it seems that, once again, the goalposts have shifted.

At the end of this year an easy way to convert civil partnerships into marriages will come into effect, and lots of couples are expected to take advantage of it. Many suspect that civil partnerships will die out entirely as soon as this process is available, leaving only a vague sense of their own pointlessness behind. Perhaps Cameron therefore sees the extension of civil partnerships as a waste of time and effort. But in making such assumptions he is naive about what civil partnerships mean to a lot of people. Labour might have created them as little more than a marriage equality consolation prize, but in doing so they accidentally made something genuinely worth having.

In Holland and New Zealand, where civil partnerships are open to heterosexual couples, the uptake is about 10%. That is a significant proportion (the Sunday Times estimates that if it were replicated in Britain it would mean 28,000 couples) who have presumably given more than a passing thought to the way in which they legally commit themselves to another person. These are straight people – thousands of them – who have never had to put up with a consolation prize. They have opted in to commitment but out of marriage, and there are many good reasons why they might have done so.

In Britain, civil partnerships are virtually indistinguishable from marriages: state benefits and pensions remain much the same. But there are a few key differences (and I'm not talking about the strange-but-true fact that you can dissolve a marriage, but not a civil partnership, if one partner is found to be "suffering from a venereal disease in a communicable form" at the time of union.) Civil partnerships, essentially, strip away all compulsory ceremony from the proceedings: no prescribed form of words has to be uttered at a ceremony, for instance (which have to be said in the case of all marriages, even at registry offices.) That's not to say that you can't put on your own (amazing) party and say your own vows, it's just that you have the choice not to.

Importantly, civil partnerships also include the names of both parents of each partner on the certificate, rather than merely the names of the fathers. This is what sells civil partnership to me most as a heterosexual woman: the fact that the institution of marriage is still saturated in sexist trappings and traditions that once recognised women as less legitimate and less equal to their partners. You may not have to walk down the aisle in a white dress shaped like a meringue and be "given away" by your father to your husband like property (unless that's your bag), but there's no escaping that marriage was a man-to-man transaction for hundreds of years. The father-only certificate is the irritating hangover of that long tradition of women-as-chattel. For a lot of us, that reminder is enough to make us want to opt out altogether.

Civil partnerships are modern unions created in a time where sex discrimination was illegal rather than actively encouraged. For heterosexual couples who want to avoid "husband and wife" but stick with "partners", leave behind the bad track record of marriage but make a legal commitment to one another in the presence of their family and friends, this should be available. Because until we have partnership equality and true choice across the board, we are putting ourselves to shame. One might wonder why we should allow a government led by the disastrous partnership between Cameron and Clegg to dictate the nature of our own.