As far as happy and stable families go, I am luckier than almost everyone I know. Since I was a child, I’ve known that I would never have to stomach my family being cleaved in two, because the two people who raised me were entirely committed – both to each other, and to me.

These days, when I go back home (very regularly), I am met with two loving and financially interdependent best friends who have lived together happily for the last 24 years in a co-owned home with co-owned cats, and show no signs of restlessness. Now they’ve retired, they’ve even taken up playing Tuesday bridge together.

So far, so sickeningly idyllic – but 24 years ago it wasn’t so.

When my mum found herself pregnant in the early 1990s, she, like so many women in the same situation, faced the prospect of a tough future. Living with my biological father wasn’t an option, and though she was working hard to scramble up the career ladder, she wasn’t rich, and certainly couldn’t afford much (ludicrously expensive) childcare. Even if she somehow did find a way to juggle all the varied responsibilities of parenthood on her own, she knew she’d spend a lifetime battling the stigma of being a single mother.

All in all, “little whoops”, as I was affectionately known, seemed like something of a nightmare.

Luckily for everyone, my wonderful aunt stepped in. Without missing a beat, she gave up her financial independence and single London life to become a second parent to her younger sister’s child.

In the 24 years since then, the three of us have formed as stable a family unit as anyone could possibly wish for. I’ve never considered my aunt as anything other than a parent, and I couldn’t say I feel any closer to one sister than the other. To anyone who knows us, the idea that we “aren’t a family” would seem absurd.

But the law says otherwise.

The sisters who raised me have no legal means by which to make their relationship official, meaning that they are exempt from the rights afforded to civil partners and married couples; most importantly the right to inherit a joint tenancy, and the right to pass on a jointly owned home to each other free of inheritance tax.

Despite demonstrating twenty-four years of loving commitment – and raising a child together – my mum and aunt, and tens of thousands like them, have fewer privileges than a couple of 19 year olds who got hitched on holiday and tied the knot “for the lolz” on a drunken night out.

In their case, this means that if one of them died, the bereaved sister would have to sell our family home (which they’ve lived in since I was a toddler) immediately, in order to pay the inheritance tax on the deceased sister’s share. According to our calculations, the sum the government would extract from her would be roughly equal to the original joint mortgage they took out in 1995, and have been paying back all their lives.

The cause of this glaring injustice can be traced back to the early 2000s, when Tony Blair found himself in a social policy quandary. The then Prime Minister had spent the whole of his political career marketing himself as the Modernising Messiah, and so naturally, the LGBT community considered him something of a kindred spirit. When they came to him in 2003 requesting the same rights as heterosexual married couples, they assumed it would be an easy sell.

Unfortunately for Blair, although he was keen to help, the 2005 election was on the horizon, and election time meant keeping a few social conservatives sweet. The result of this dilemma was the Civil Partnerships Act of 2004. The legislation – ingenious in its way – allowed gay couples a type of union which afforded them the same rights as straight couples, without having to open the same-sex marriage can of worms at a politically delicate moment.

As an interim solution to a thorny problem for a centrist Prime Minister, civil partnerships worked a treat. As a serious piece of legislation, they’ve been – to put it mildly –  problematic. When same-sex marriage was introduced in 2013, civil partnerships (civil marriages in all but name) became obsolete for those in a romantic relationship, but because reversing legislation is a time-consuming and expensive process, the civil partnership act of 2004 stayed in the statute book.

That means that in 2017, same-sex partners – or even same-sex platonic friends – who wish to formalise their relationship have two methods of doing so (via a civil partnership or a civil marriage), straight couples have one (civil marriages) but committed, loving, financially interdependent cohabiting siblings don’t have any way at all. Although there is nothing in the law to dictate that civil partnerships must be between people in a sexual relationship, because the legislation was historically used as a proxy for same-sex marriage, cohabiting siblings remain exempt.

According to Rebecca Stenfeld and Charles Keidan the injustice in the situation is that straight couples must get married in order to formalise their relationship. In an article for The Telegraph last year, the pair wrote that they “didn’t want all the social pressures and expectations that surround marriage, like the bride wearing white virginal dresses and being given away by her father”, so wanted to opt for a civil partnership instead. In their book, the exemption of straight couples in the civil partnerships act is a “breach of their human rights”, and they are being “discriminated against for their sexual orientation”. They are stepping up their battle and taking it to the supreme court early next year.

If you are ever looking for an illustration to explain what a “first world problem” is, look no further than this pair of London academics. They are well aware that a civil marriage – which would give them exactly same rights as a civil partnership – does not require a bride to wear a “white virginal” dress or be given away by her father, and that if Rebecca so wished she would be more than welcome to walk down the aisle clad in a bikini and accompanied by her pet flamingo, but they seem to be ignoring this reality in order to legitimise their outrage. The “social pressures and expectations” surrounding marriage are only a problem if they choose to bow to them, because as far as the law is concerned a civil wedding and a civil partnership are almost identical.

My mum and aunt who are also barred from civil partnerships, but clearly don’t have the cushy option of marriage to fall back on, are in a very different situation – and are facing a real injustice.

In 2004, when civil partnerships were introduced, the decision to exclude cohabiting siblings made sense. The legislation was designed to mimic marriage as closely as possible, and including siblings would undermine that aim.Thirteen years later, now same-sex marriage exists, and an increasing number of people are using civil partnerships to formalise platonic friendships, that logic no longer stands up.

In the years since same-sex marriage was legalised, rendering civil partnerships obsolete for romantic couples, there have been numerous attempts in parliament to put right the discrimination against blood relations. At every point the seriousness of the injustice has been acknowledged. At every point it has been ignored.

Now, after much campaigning, my mum and aunt have succeeded in getting a Private Members’ Bill in the House of Lords, which would, if passed, open up civil partnerships to long term cohabiting siblings. On 3rd July, it was revealed that the “Siblings Couple” bill (as it is called) is 22nd out of 60 on the ballot for second readings in the Lords, which means that the chances of it being debated properly this parliament are reasonably good.

Such legislation would be a very important first step towards ending the current mindless discrimination against all those siblings in platonic relationships who choose to live together a friends/companions/co-parents, but who are currently denied all the basic legal safeguards and fiscal protections which make that choice an easy one.

There’s a long way to go, but the journey has begun.

Watch this space.