Unmarried couples could be ordered to sell their homes, pay lump sums and share pensions in the event of a break-up, the Government's law reform advisors said yesterday.
The Law Commission said the two million cohabiting Britons should be able to make financial claims against each other in some circumstances.
A partner should generally be able to make a claim if they made "economic sacrifices" during the relationship, such as giving up a career to raise children, and the benefits were unfairly shared at a split.
The commission said the new set-up would apply to heterosexual and gay couples who had been together for a minimum period, but it did not set out what the minimum should be.
It also recommended allowing couples to opt out of being liable to the new rules providing they signed a written agreement.
The measures would be "more limited in scope" than divorce laws, but the courts would be able to order the sale of property, lump sums, monthly payments, pension sharing and interim payments.
The commission also said it favoured the clean break principle used in divorce laws, which sees claims settled quickly by transferring the family home or a lump sum to a partner.
Applicants would have to show that their contributions and economic sacrifices during the relationship would otherwise be unfairly shared on separation, said the report.
The commission, headed by High Court judge Sir Roger Toulson, insisted the measures would not damage the institution of marriage.
They could encourage more people to wed because people would no longer avoid financial responsibilities to their partners by living together, it suggested.
The commission said couples with children should automatically be eligible for settlement. But it asked people responding to the consultation paper to give their views on whether the same should apply to stepchildren.
Misconduct or fault by either partner should not normally play a big part in deciding a financial deal, it added.
The paper said Government predictions forecast that by 2031 there would be 3.8 million cohabiting couples and fewer than ten million married couples.
Sir Roger said: "At present, there are too many cases where unfairness can occur because of the way people have lived together.
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