A Birmingham lawyer has called for the urgent reform of the law relating to cohabitees, claiming it is outdated and unfair.
Geoff Wood, a partner and head of the private client team at Birmingham firm Coley & Tilley, says there is no adequate legal protection for the two million couples currently living under the same roof.
Following a break-up, if a couple are married, both spouses have a right to ask for maintenance, a lump sum, for property to be transferred in to their name or to be sold and the proceeds divided, and for pension sharing orders.
In contrast, a cohabitee does not have any such rights.
Men or women who move in with a partner can take some limited steps to protect their interests. For example, they can ensure that their home is in joint names. If a couple elect to hold the property as joint tenants, if one dies the other automatically becomes the owner of the home.
But other rights, such as exemption from inheritance tax, are only available to married couples. This applies even where any accumulated wealth was created jointly.
Mr Wood said it came as a surprise to many that the law is so different for people who have chosen to live together, rather than marry.
"The law is out of step with modern relationships. The number of women who cohabit before marriage is now 70 per cent in England and Wales. This means that thousands are vulnerable in the event that their relationship breaks down."
However, Mr Wood believes it is only a matter of time before increased legal protection over property rights is extended to unmarried couples.
He said: "The Law Commission is currently reviewing the property rights of couples who share a home and the financial injustices which may arise when the relationship ends.
"However, it is unlikely that the Government will put cohabiting couples on the same footing as married couples. This could be seen as undermining the institution of marriage and could be unpopular with church and family groups.
"The recent introduction of the Civil Partnerships Act was designed to extend such protection to gay couples. This demonstrates that the Government isn't afraid of a little controversy.
"What's more, the idea is not necessarily to give cohabitees the same rights as married couples, but to give them some protection. The issue is how to deal with financial hardship if a relationship breaks down."
In the meantime, Mr Wood urges couples to draw up a cohabitation agreement.
This will determine how the assets are to be divided in the event of a breakdown in the relationship.
He said: "The cost of this could be circa #500. As well as clarity on how the assets are to be divided, this also buys you considerable peace of mind."
David Pickering, an expert in family and matrimonial law at leading law firm Cobbetts, noted: "Many cohabiting couples are making financial arrangements that they simply don't understand and are much less protected than those who are married or in civil partnerships.
"We have been dealing with cases where one cohabitee has made a large cash investment in a property on the understanding they will get this back if the property is sold, but they are not signing any documents to formalise this and many are having a nightmare if a relationship breaks down.
"We cannot say strongly enough that cohabiting couples need to know exactly what they are signing when moving in together, no matter how un-romantic that might sound."