One in six couples in Britain live together without getting married.
Dawn and Andy: why can't the law be changed?
Many are in long term relationships and might describe their other half as a partner or a common-law husband or wife.
But, legally there is no such thing as a common law relationship, say campaigners from the organisation Advicenow.
And many couples are living in blissful ignorance of how few rights they have over property, inheritance and children, when relationships break down or partners die.
Breakfast talked to Martin Jones, of the website Advicenow and to one couple who've decided not to marry
Dawn Williams and Andy Balman have been living together for 15 years. They have three children - but got a shock when they decided to make a will.
Andy discovered he had no rights over the children, even though they had his surname: Dawn had full control, because they'd never married.
Dawn and Andy still don't plan to get married - but they would like to see the law changed, to give unmarried couples more rights
Couples who live together may feel married, but without that piece of paper, they just don't have the same rights, says Advicenow.
The report found that many couples were wrong on a number of issues about cohabiting:
61% of people wrongly believe that couples who have lived together for a while have the same rights as married couples.
65.4% of women wrongly believe that they have the legal right to financial support from their partner if they have been living together over five years.
77.4% of people wrongly believe that the father of a child automatically has a right to make decisions about his child's future, regardless of whether or not he is married.
47.9% of respondents wrongly believe that if one of a cohabiting couple of over five years died without making a will, the surviving partner would automatically inherit what was left behind.
In fact, the Queen is more likely to inherit than the partner.
68.3%t of 25-34 year-old respondents - the people most likely to cohabit according to the survey findings - wrongly believe cohabiters have the same rights as married couples.
One in six couples cohabit - this is equal to 25% of British couples aged between 16 and 59.
The Advicenow website spells out the complete legal position and the difference between the rights of un-married, and married couples living together.
But un-married couples face more complications if one partner dies or the relationship breaks up.
The Advicenow website will tackle different issues each month including How to make a 'Living Together Agreement', who has parental responsibility, and how to how to appoint a guardian.
Think you know your rights?