Couples who are living together should have more legal rights, according to a report by the Law Commission.
Cohabiting couples do not have the same rights as married couples
It says the 2.2m cohabiting couples in England and Wales should have more protection if they split up.
It does not suggest cohabiting couples get the same rights as married ones, but says they should be able to make a financial claim if they break up.
Ministers are studying the proposals but some critics complain they amount to a "kind of marriage lite".
The Law Commission suggests couples without children should have lived together for at least two years for them to be able to make a financial claim.
Any financial compensation would be based on the contribution to the relationship, and the scheme would allow for couples to opt out.
Unlike in divorce, there would be no principle for co-habiting couples that assets should be shared equally, and no ongoing maintenance payments.
But it would mean that if, for example, a partner has given up a career to bring up children, they should receive compensation if the couple separates.
The Law Commission advises the government on legal reform.
Stuart Bridge, the law commissioner responsible for the reforms, said current law for dealing with property disputes was "unclear and complicated".
It often caused serious hardship for not only the couple, but their children too, he said.
He rejected claims such reforms would undermine marriage.
"We consider our scheme strikes the right balance between the need to alleviate hardship and the need to protect couples' freedom of choice."
But Jill Kirby of the Centre for Policy Studies criticised the plans as introducing a "kind of marriage lite".
"If a man and a woman want to create a family together, then the most durable contract available to them is marriage," she said.
"If they decide not to marry, then I think consequences must flow from that, and that if we introduce... a kind of substitute version, as the Law Commission proposes, then it does detract from that institution and I think will lead to more confusion."
And Richard Kane, founder of National Marriage Week, said although he personally thought people should marry rather than cohabit, he disagreed with the state "interfering" with cohabiting couples in such a way.
"We think a much stronger way to do this would be for a couple to actually have to make a choice to go and sort of make a registration if you like....
"I am concerned about the state interfering then by default."
The commission said many believed in the "common law" myth - the idea that partners would be entitled to a share of the assets when a relationship broke down.
However, at present, cohabiting couples have very little legal protection.
The report was two years in the making and builds on a consultation paper published in May 2006.
A similar rights package was introduced in Scotland in May last year.