The government has indicated it could scrap civil partnerships altogether as it considers the future of the legal union.
A newly-published document published by Secretary of State for International Development Penny Mordaunt suggests that the government could abolish the institution should take-up rates among same-sex couples remain low following the introduction of equal marriage in 2014.
Civil partnerships were first introduced in 2004 under Labour, with thousands of same-sex couples taking the opportunity to formalise their relationships in the eyes of the law before marriage equality was legalised a decade later.
However, the number of same-sex couples opting to enter civil partnerships has dropped since the introduction of marriage equality, with just 890 civil partnerships registered in 2016 in England and Wales compared to 6,305 between 2007-2013.
The new report states: "If demand for civil partnerships remains low and this becomes a stable position, this might suggest that same-sex couples no longer see this as a relevant way of recognising their relationships, and that Government should consider abolishing or phasing out civil partnerships entirely."
It goes on: "If significant demand for civil partnerships remains over time, this may indicate that the institution still has relevance."
The memo comes as the Supreme Court hears the appeal of a heterosexual couple who want the right to enter a civil partnership on Monday (May 13).
Rebecca Steinfeld, 37, and Charles Keidan, 41, are challenging the ban on mixed-sex couples entering civil partnerships as outlined in the Civil Partnerships Act 2004.
The campaign to open civil partnerships to mixed-sex couples has been backed by veteran LGBT+ rights campaigner Peter Tatchell
The couple, whose campaign has been backed by veteran LGBT+ rights campaigner Peter Tatchell, were defeated in the Court of Appeal in February last year after the panel ruled that the goverment should be given more time to examine the issue. The pair were later granted the right to appeal to the Supreme Court.
In its latest report, the government says it will continue to monitor the number of same-sex couples entering civil partnerships until September 2019, before launching a full public consultation on the issue in 2020.
However, should the Supeme Court rule in favour of Ms. Steifeld and Mr Keidan on Monday, the government could be compelled to start opening civil partnerships to heterosexual couples immediately.