As a family lawyer, I know the impact the Supreme Court ruling in favour of unmarried couples will have

The judgment underscores that the responsibility for a change in the law around cohabitants lies with the legislature

Siobhan McLaughlin has fought a desperate battle since her partner, John Adams, died in 2014. Ms McLaughlin applied for a widowed parent's allowance to help support her and their four children, but her application was refused because she and Mr Adams were unmarried. Despite living together for 23 years and raising a family, the law states that the widowed parent's allowance is only available to surviving spouses or civil partners.

Ms McLaughlin's predicament is one shared by many families in the UK. Unmarried couples, also known as cohabitants, are the fastest growing family type in the country, according to the Office for National Statistics (ONS).

The number of unmarried couples living together has doubled in the last 20 years. Of the 19 million families in the UK, 3.3 million are cohabiting and many of these families are unaware of the risks they face.

McLaughlin's case has been supported by the Supreme Court, which has ruled today that the Northern Ireland Department for Communities' decision not to pay her the widowed parent's allowance contravened her rights under the European Convention on Human Rights. This is a welcome victory for McLaughlin in a long-running and no doubt emotionally taxing dispute. It is a positive outcome for other unmarried couples in England and Wales too, suggesting that they have sound legal grounds to assert their rights and receive the same protection and benefits as married couples.

But cohabiting families should be wary of drawing too much comfort from the Supreme Court's decision. The judgment makes clear that the justices reached their conclusion based on the specific facts of McLaughlin's circumstances and the particular benefit she was claiming. The widowed parent's allowance is targeted primarily at the needs and well-being of children.

The justices agreed that the law should not discriminate between the children of unmarried couples versus the children of married couples. However, the justices also said there may be other circumstances where married couples would justifiably receive preferential treatment.

McLaughlin had to take her case all the way to the Supreme Court precisely because unmarried couples are currently left drastically under-protected by family law in England and Wales. This lack of protection threatens their security whether one of the couple dies or the couple separates, and leaves the whole family, including children, exposed to potentially severe financial hardships. In brief, unmarried couples have no legal right to each other's property or assets, unless they have legally recorded this in some form, and no statutory right to ongoing financial support from their ex-partner if they separate.

Unfortunately, this vulnerability is not as well-known as it should be. The concept of “common law” husbands or wives remains popular, and can lull couples into a sense of security that is exposed under the most difficult circumstances. Family law practitioners and organisations have long campaigned for a change in the law, and a number of cases like McLaughlin's have provided judicial support to these campaigns. The judgment underscores that the responsibility for a change in the law around cohabitants lies with the legislature.

Social attitudes surrounding marriage and children have been evolving for some time, as demonstrated by the ONS's statistical tracking. The law needs to be changed to reflect and support this, or it risks standing still and failing to cater for the needs of modern families.

Sarfraz Ali is a solicitor working in the divorce and family team at Withers law firm