How we split: It's not just divorcing couples. Now even unmarried partners are heading for the courts

People who live together instead of getting married will get the right to share each other's money and property if they split up, under new proposals to be published this week.

Rather than having to walk away with only the CDs they had in the first place, a change in attitudes would allow Britain's 4.4 million opposite-sex cohabitees to stake a claim for possessions acquired together and wealth that has been built up while in a relationship.

The Law Commission, an independent body set up by Parliament to recommend change where it is needed, is likely to say unmarrieds should no longer lose out financially when their relationships break down.

"We have now reached the stage where it cannot be left any longer," says Vanessa Lloyd Parry, a solicitor specialising in family law. Increasing numbers of people are choosing not to get married, and the introduction of civil partnerships for gay and lesbian people has increased the pressure for legal change. "If you recognise the rights of same-sex couples who cohabit, then it cannot be right to discriminate against heterosexual couples in the same situation."

Such a move has been resisted until now because of pressure from religious groups not to undermine marriage. But The Independent on Sunday has learnt that ministers are to seriously consider the commission's proposals, because they believe the time is right to revamp the law. One senior minister said many couples who were not married did not realise they had no claim on a property or the income of their partner. "There is a problem. We are going to look at this seriously. That is why we have commissioned the report."

One particular concern is that children born out of wedlock may not have protection or even a home to live in if their parents break up. Women who have lived with their partners for 20 years can find themselves penniless because of their lack of rights. Officials at the Department for Constitutional Affairs have been told to re-examine the issue.

The Law Commission's consultation document will not go as far as giving cohabitees exactly the same rights as marrieds, but it will suggest that a financial safety net is put in place. Some lawyers favour a sliding scale so that the longer you stay together, the more rights you acquire, until the length of relationship means they are almost marital.

So what does this mean in real life? Deborah, a 37-year-old lecturer from London who does not want her surname published, bought a flat with her boyfriend after they had been living together for two years. She paid the deposit and an equal share of the mortgage, but received less than half the sale price when the pair went through a painful separation six years later.

"We had renovated the property, and the sale made a lot of money, but I received much less than I had expected," she said. "I only received a fraction."

Deborah now wishes that she and her boyfriend had got married, because it would have left her in a far stronger financial position. "It's not the most romantic thing in the world, but people must discuss these things if you are thinking of moving in together. You need to know what your rights are."

Her biggest mistake was to assume that she had rights as a "common-law wife", only to learn too late that no such rights exist. "I lost more than £25,000, and had to stay with a friend for more than a year before I got myself financially established again," she said. "I didn't go to court because the situation between us was bad enough already, and I just wanted to get it over with. I'm not sure if I would even have had a legal case to argue because there was never anything in writing."

At least there were no children. Divorcees have an automatic right to maintenance so they can feed and clothe their offspring, but unmarried mothers who split from their boyfriends have to make their case to a judge and any financial support they win is only temporary. A mother can make a claim against her former partner under the Children's Act, but only as long as her sons or daughters are underage. Any money awarded to pay for a home has to be paid back to the father when they reach 18.

Sandra Davis, a leading family law expert, says many people make the same mistake as Deborah. "They believe that the provisions for a couple who separate after cohabiting are akin to those in divorce, but that is not the case at all," said Ms Davis of Mischcon de Reya. "What the Law Commission is trying to do is create some kind of safety blanket after a minimum time of cohabiting. The question is how long after a couple starts living together should that come into effect."

The landmark legal case was Burns vs Burns in 1984. Patrick and Valerie Burns lived together for 19 years, and raised two children, but never married. They bought a house in Patrick's name, and Valerie made no financial contribution to the deposit or mortgage. The couple lived in the house for 17 years and, when they separated, the wife claimed the house. Her claim was rejected. The case was upheld by a House of Lords ruling in 1988.

Society has altered a great deal since then. The number of people getting married has fallen, and the number of marriages that fail has risen to one in three. Now 40 per cent of births take place outside marriage, which is four times more than was the case in 1986. The number of cohabiting couples who are living with children has gone up by 50 per cent since 1996, to 2.2 million.

The British view of marriage has changed dramatically. And the past week has seen two major legal rulings which shift our perspective on it again, in a substantial way. They involved huge amounts of money, being fought over by men and women who had grown very rich together, but the cases will affect the lives of tens of thousands of less wealthy people by establishing that a woman who stays at home while her husband works has the right to claim a substantial share of the wealth he creates.

The Law Lords ruled unanimously in favour of Melissa Miller, who was demanding a £5m settlement from her ex-husband, a City fund manager. They also agreed that Julia McFarlane, who gave up her career to be a wife and mother, should receive £250,000 a year for life from her high-flying husband.

Until now, levels of maintenance were set according to her needs, plus an equal share of the value of the family home. Women in short marriages were restored to their standard of living before the union. But lawyers say the cases of Miller and McFarlane mean a wife can now claim an equal share of the family wealth, regardless of the length of the marriage or the financial contribution she has made personally.

David Allison of Resolution, the new name for the Solicitors' Family Law Association, says the law needs to catch up in the same way for cohabitees. "In a time when we're seeing divorce settlements like Miller and McFarlane, cohabiting couples are unable to make any financial claims at all. The difference is stark."

Additional reporting by Marie Woolf

Test case study: If Charlotte threw out Gavin...

Charlotte Church

What she has now: Last year her company Charlotte Church Ltd registered assets of £3.7m. Since then, her trustees have invested parts of her fortune in jewels, shares and property, including the house in Cardiff which she bought in 2005. With sales from recent singles and a six-figure book deal, her personal wealth is estimated at around £7m.

Record sales: £1,850,000

Two-book publishing deal: £600,000

Advertising deal with Walkers crisps: £100,000

Five-bedroom house in Cardiff: £750,000

Registered assets of Charlotte Church Ltd: £3.7m

Total estimated wealth: £7m

Gavin Henson

What he has now:

Since 2004 he has earned £120,000 a year with the Ospreys rugby team and has sponsorship deals with Nike, Mercedes, EA Games, Webb Ellis balls, Gillette. Last year he signed a two-book publishing deal with Harper Sport.

Two seasons playing with the Ospreys: £240,000

Sponsorship deals: £1m

Publishing deal: £100,000

Advertising deals: £160,000

Total estimated wealth: £1.5m

What she would get:

Under proposed new rules for cohabiting partners, a court would determine if either partner had suffered any economic loss because of the relationship. If a judge accepted that his rugby - and his earning potential - had suffered due to Church's hard-partying lifestyle, Henson's claim against Church could reach up to £2m.

She would be left with: £5m

What he would get:

Fellow players have claimed that Henson spends more time accompanying Church to film premières and nightclubs than he does on the training circuit. If the couple were to separate, Henson could theoretically allege that the relationship damaged his professional career.

He would be left with: £3.5m

The Law: Who gets what when cohabiting couples break up

More than two million couples cohabit in England and Wales, though they still have fewer rights than married couples. Most have a mistaken belief in "common-law marriage", though no such thing has existed since 1753.

Vanessa Lloyd Platt, a divorce and matrimonial lawyer who has practised for 28 years, says: "People like me have to tell them that after 17 years of living with someone they have no rights whatsoever."

If one partner dies before making a will, the other has no automatic entitlement to anything. Where either partner leaves a will, the estate is subject to inheritance tax, whereas the estate of a married couple is not. Where a tenancy is only in one partner's name, the other has no rights.

Cohabitees gain no rights to property already owned by their partner, no matter how much they contribute to the mortgage.

In the cast of most benefits, cohabiting couples are treated the same as their married counterparts. But benefits based on National Insurance contributions do not follow the same pattern. Couples who live together have no right to each other's pensions. Bereavement and Widowed Parent's Allowances and the single Bereavement Payment cannot be paid to the surviving partner.

Mothers automatically have parental responsibility for children; in unmarried couples, the father does not. On marriage, fathers gain parental responsibility. Regardless of parental responsibility, all parents are obliged to support their children financially.

4.4m MILLION PEOPLE live together without being married

2m UNMARRIED COUPLES have children living with them

50 THE PERCENTAGE of cohabiting couples who are aged under 35 years.

13 THE PERCENTAGE of unmarried couples with children who profess to be athiest

Source: Office of National Statistics