Emily Thornberry, the shadow attorney-general, has committed a future Labour government to reform the law on cohabitation.

Given that the Law Commission for England and Wales recommended the law to be updated as long ago as 2007, finally cohabitants could be protected from financial injustice on relationship breakdown and being made destitute after many years of living together.

To ensure a speedy and easily understood updating of the law, cohabitants should be given the same rights as married couples on divorce, provided that either they live together for two years or have a child together and live together.

The Law Commission’s 2007 report did not include a draft bill to change the law. It only made various recommendations to be considered further. While some may be tempted to introduce lesser rights than on divorce for cohabiting couples, that will lead to new legal concepts, complexity and inevitably litigation and uncertainty.

That may be good for business for lawyers, but a disaster for cohabiting couples. Leading academics rightly pointed out the problems and pitfalls with such concepts. The Scottish law giving cohabitants lesser rights than divorcing couples since 2006 has been criticised as being hard to understand and difficult to use in practice.

Lawyers and judges up and down the country are familiar with the law on asset division and spouse maintenance on divorce. The simplest, fairest and quickest way of remedying financial injustice suffered by many cohabitants on relationship breakdown is to work with that well-known law.

Australia already has such a law for “de facto relationships” or cohabitants. That law has been in force since 2009. So has New Zealand. When it comes to family law, England and Wales tend to follow Australia, as is the case with the Child Maintenance Service, and more recently no-fault divorce.

There already exists in social security law a well-known definition of cohabitation — the six “signposts” from 1982 and before. State benefit offices up and down the country routinely assess whether a claimant is cohabiting or not, with a view to ending state benefits. The 2000 spouse maintenance case of Kimber v Kimber expanded these to eight hallmarks.

If a Labour government wants to introduce lesser rights for cohabitants on relationship breakdown than on divorce, that will lead to years of delay, injustice and uncertainty. There would be endless debates about how the law should be different from on divorce. That could delay legislation by several years.

What cohabitants need is an end to the injustice they suffer now and quickly, not in three, five or more years’ time.

Mark’s article was originally published in The Times, here.