A heterosexual couple with ''deep-rooted'' ideological objections to the institution of marriage continue their legal battle today for the right to enter into a civil partnership.
Rebecca Steinfeld, 35, and Charles Keidan, 40, take their case to the Court of Appeal following a defeat at the High Court earlier this year.
The academics, of Hammersmith, west London, who have 17-month-old daughter, have been in a committed relationship since November 2010.
They want to secure legal recognition of their relationship through a civil partnership, but are prevented because the Civil Partnership Act 2004 stipulates that only same-sex couples are eligible.
They argue that the Government's position on civil partnerships is ''incompatible with equality law''.
But in January a judge in London dismissed their judicial review action.
Although Mrs Justice Andrews concluded that their claim ''must fail'', she gave the go-ahead for the couple to take their challenge to the Court of Appeal because it raised issues of ''wider importance''.
Explaining her ruling, the judge said she did ''not accept'' that the enactment of the Marriage (Same Sex Couples) Act 2013 had caused restrictions under the Civil Partnership Act on opposite-sex couples entering into a civil partnership ''to become unlawful''.
In a statement issued before the latest round of the legal battle, Ms Steinfeld said: "We are going to the Court of Appeal on behalf of ourselves and the more than 70,000 people who have signed our petition calling for civil partnerships to be open to all.
"Those people will have lots of different reasons for choosing not to get married: from personal experiences to principled objections, to simply not feeling ready.
"It's not for the Government to dictate how couples choose to formalise their commitment, but it is for the Government to ensure all couples are financially and legally protected."
Mr Keidan commented: "The Government has everything to gain by opening civil partnerships to different sex couples.
"Civil partnerships offer the possibility of legal protections and family stability for three million unmarried couples - the fastest growing family type in the UK.
"Civil partnerships already exist for same-sex couples. It would now be fair, straightforward and popular for the Government to extend them to everyone."
Their case will be heard by Lady Justice Arden, Lord Justice Beatson and Lord Justice Briggs.