There is a popular myth - around 59% of unmarried couples believed it in 2000 - that cohabiting couples are "common law" husbands and wives, and that the law protects the vulnerable party, and governs how property is divided in the event of a break up, a bit like divorce, writes Sandra Haurant.
In fact, under current legislation, unmarried heterosexual couples and gay couples who have not gone through a civil partnership ceremony have very few rights.
If a marriage breaks up, a partner has the right to claim maintenance payments, a cash lump sum, transfer of property into their name or for property to be sold and the proceeds divided, as well as a portion of their ex-spouse's pensions.
Married couples also get a variety of tax breaks. They can also transfer assets between spouses without having to pay capital gains tax, for example. And when a person dies, their widow or widower is not liable to pay inheritance tax on the estate.
For unmarried couples, these rules do not apply. There are no freebies, no tax breaks to be had. If a person dies, the surviving partner has to pay full inheritance tax at a rate of 40% over the threshold of £285,000. In fact, if one half of an unmarried couple dies without a will, the surviving partner cannot automatically expect to inherit the estate.
The Law Commission's 370-page consultation paper for a bill to protect unmarried couples aims to change this. Under its suggestions, partners who have lived together for some time, perhaps two years, will be able to make similar financial claims to divorcing couples.
Cohabiting couples will no doubt be pleased to benefit from the same financial advantages as married couples. And with 4 million people cohabiting, there will inevitably be many cases of injustice, financial and otherwise, when relationships break down, and therefore people who need the law to protect them.
There are an estimated 2 million unmarried couples living together in the UK, and this number is expected to almost double by 2031 to 3.8 million. The pro-marriage lobby argues that the Law Commission's plans undermine marriage to the point of threatening to destroy the institution completely.
When you get married, you choose to involve the state in your personal relationship with your partner. You make a formal commitment. You sign papers. There are witnesses.
As last week's high-profile cases demonstrated, when it comes to the law, divorce and money, your relationship, or breakdown thereof, becomes other people's (very lucrative) business. When you decide not to get married, you choose to leave the state out of it. Should the state stay out of your break-up too?
