A heterosexual couple may struggle in their attempt to register as civil partners.

Should a man and woman be able to register as civil partners? More to the point, should the courts allow them to do so? And, even more pertinently, should taxpayers pick up the bill?

These questions are raised by a judicial review claim lodged before Christmas by Rebecca Steinfeld and Charles Keidan, both academics, who have been in a ‘committed opposite-sex heterosexual relationship’ for four years. They decided to formalise their relationship but did not want to marry. So they announced their engagement in the forthcoming civil partnerships section of the Jewish Chronicle and set off to give notice at Chelsea register office.

That was as far as they got. As the registrar reminded them, section 3 of the Civil Partnership Act 2004 says that ‘people are not eligible to register as civil partners of each other if they are not of the same sex’.

The 2004 act was introduced to allow gay couples to enjoy a status broadly similar to marriage. It was followed by the Marriage (Same-Sex Couples) Act 2013, whose purpose is summed up in its title. Since last month, civil partners have been able to convert their relationship to marriage. It is the government’s view that opposite-sex couples do not need civil partnerships because they can live together or marry in a religious or civil ceremony.

‘As a couple committed to full equality between the sexes, [Steinfeld and Keidan] wished to avoid the patriarchal rituals associated with marriage’, their claim form said. Asked on Radio 4 what these rituals might be, Keidan referred to ‘the idea of the father giving away his daughter and ideas of ownership’. Steinfeld argued that a marriage certificate was good evidence of a wife’s change-of-name but not of a husband’s.

This strikes me as inconsistent with marriage as it has now been redefined. Where is the patriarchy in a marriage between two men? What is to stop two women using their marriage certificate as proof that they have changed their names?

What matters, though, is the law. The couple have briefed Karon Monaghan QC, one of the leading practitioners in the field. But I still think they will have something of a struggle.

Monaghan’s first argument is that the Royal Borough of Kensington and Chelsea, for which the registrar worked, was acting in breach of the Equality Act 2010, which prohibits a public authority from treating a person less favourably on grounds of sexual orientation. The argument, presumably, is that only a gay couple can register a civil partnership.

But it is not your sexual orientation that governs your eligibility for a civil partnership: it is your sex. Two unrelated straight men can register a civil partnership if they want to take advantage of the tax benefits. Steinfeld and Keidan could not become civil partners even if one of them was gay.

The next problem, as Kensington council points out, is schedule 22 to the Equality Act, which allows discrimination on grounds of sex or sexual orientation if it is done ‘pursuant to… a requirement of an enactment’. The enactment in this case is section 3 of the 2004 act.

Ah, says Monaghan, but the Equality Act must be read compatibly with the human rights convention ‘so far as it is possible to do so’ – as the law lords famously did in 2004 when they decided that a surviving gay partner could inherit a Rent Act tenancy in the same way as a person who had been living with the deceased tenant ‘as his or her wife or husband’. But it is one thing to treat a homosexual cohabitant in the same way as a heterosexual one; it is quite another to disapply schedule 22, as the couple are demanding.

Monaghan’s second argument is that the Civil Partnership Act is incompatible with the right to respect for a person’s private life, which must be enjoyed without discrimination. Short of rewriting the act, the most that Monaghan can expect is a declaration of incompatibility, passing the buck back to an unwilling government.

And it is the government, she says in her third ground, that has failed to comply with its public sector equality duty. But that merely requires public authorities to have ‘due regard’ to eliminating discrimination.

In the end, money must be the biggest hurdle for Steinfeld and Keidan, who are expecting their first child. Although they have paid around £4,000 towards their lawyers’ fees and raised more than £7,000 through crowdfunding, they say they cannot go to trial without a protective costs order, exempting them from paying the costs of the council and the government even if they lose.

Such an order is not normally granted when the applicant has a private interest in the outcome of the case. So it looks as if they will just have to take the law as they find it.