The first heterosexual civil partnerships have taken place (Wiktor Szymanowicz / Barcroft Media via Getty Images)

The first mixed-sex civil partnerships have taken place, after they were opened up to straight people.

Civil partnerships were initially introduced in 2004 as a segregated form of union available only to same-sex couples, and continued to exist after equal marriage became law in 2014.

Straight couples enter civil partnerships for first time

However, the UK government was forced to open them up to all couples after mixed-sex couple Rebecca Steinfeld and Charles Keidan won a Supreme Court battle on the issue.

The first straight civil partnerships took place on New Year’s Eve, December 31, allowing straight couples to enter a legal form of partnership without becoming husband and wife.

Steinfeld and Keidan were among the first couples to enter a civil partnership, attending a registration ceremony at Kensington and Chelsea Register Office.

According to Sky News, Steinfeld told reporters: “Today, as one decade ends and another dawns, we become civil partners in law.

“Our personal wish to form a civil partnership was rooted in our desire to formalise our relationship in a more modern way, focus on equality, and mutual respect.

“So today is a unique, special and personal moment for us, a moment that we’ve been able to affirm our love and commitment to one another in the company of our beautiful children, Eden and Ariel, and close friends.

“And have that love and commitment given legal recognition in a way that best reflects who we are, what we love and the life we value.”

Other mixed-sex couples – including Cathy Brown and John Grisswell from Derbyshire and Mary Ann Lund and Gareth Wood from Market Harborough – entered civil partnerships on Tuesday.

Lund told the BBC: “It’s more about the equality of a partnership rather than a marriage.

“That’s something important to us, that we feel there is a kind of historical, patriarchal baggage in marriage and it’s not particularly something that’s for us.”

LGBT+ campaigners supported move to expand civil partnerships

The move to open up civil partnerships was supported by LGBT+ charity Stonewall and equal rights campaigner Peter Tatchell.

Tatchell said: “I am delighted that we have finally won heterosexual equality in civil partnership law.

“In the Netherlands, where equal civil partnerships have co-existed alongside marriage for two decades, a majority of straight couples get married but about a sixth opt for a civil partnership instead. I would expect a similar take up rate in the UK, especially among young couples who see civil partnerships as more egalitarian and not associated with the religious and patriarchal traditions of marriage.”

However, the move was contentious within some parts of the LGBT+ community, with some younger activists questioning the future of an institution seen as a legacy of inequality.