A heterosexual couple are to fight for the right to enter into a civil partnership in the UK's highest court.
Rebecca Steinfeld, 36, and Charles Keidan, 40, want to secure legal recognition of their relationship through that route, but are prevented because the Civil Partnership Act 2004 says only same-sex couples are eligible.
The academics, who live in west London, have been given the go ahead to take their case to the Supreme Court.
They suffered defeat at the Court of Appeal in February, but declared afterwards that there was still "everything to fight for".
The couple, who have a daughter and another child on the way, claim the Government's position is "incompatible with equality law".
Welcoming the latest stage of their legal battle, Ms Steinfeld said they were confident their case was "sound", adding: "We hope the Supreme Court will deliver a judgment that will finally provide access to civil partnerships for thousands of families across the country."
Mr Keidan commented: "The incredible support from many thousands of people who have signed our petition and backing from MPs across the political spectrum has enabled us to come this far.
"What started out as a personal effort to become civil partners has taken on wider significance as we realised that as many as 3.3 million co-habiting couples are affected by the status quo.
"Over the last few years, we've heard the same message: whilst most couples want financial and legal protection for themselves and their families, not all feel comfortable with marriage.
"Civil partnerships offer a legally binding arrangement that is fair, popular and good for families and children."