The belief in common-law marriage is a "massive misnomer" held by a large number of people, according to a financial planning company.
Kelvin Lillywhite, financial consultant with Best Advice, stated that a large number of the population think that if they live together for a number of years, they are in a common-law marriage.
He added that his understanding was that such a practice was discontinued "in the Middle Ages."
Mr Lillywhite added that marriage clarifies a range of topics such as benefits that individuals are entitled to with regard to pensions.
"There are a lot of pension schemes that will give benefits to spouses. They may not pay that to a long-term partner," he said.
Figures released by the Office for National Statistics released figures last week which indicated that the number of unmarried but cohabiting couples has increased by some 65 per cent in the last ten years.